The VSI C preprocessor uses directives to affect the compilation of a source file. For VSI C on OpenVMS systems, these directives are processed by an early phase of the compiler, not by a separate program. The preprocessor directives begin with a number sign (#) and do not end with a semicolon. The number sign must appear in the first column of the source line.
1 – Null directive (#)
A preprocessing directive of the form # <newline> is a null directive and has no effect.
2 – Conditional Compilation
Conditional compilation is provided by the following directives:
#if constant-expression
Checks whether the constant expression is nonzero (true).
#ifdef identifier
Checks whether the identifier is defined.
#ifndef identifier
Checks whether the identifier is undefined.
#else
Introduces source lines to be compiled as an alternative to the
conditions tested by the previous directives.
#elif constant-expression
Delimits alternative source lines to be compiled if the constant
expression in the corresponding #if, #ifdef, or #ifndef
directive is false and if the additional constant expression
presented in the #elif directive is true. An #elif directive is
optional.
#endif
Ends the scope of the previous directives.
If the condition checked by #if, #ifdef, or #ifndef is true, then
all lines between the #else, #elif, and #endif are ignored. If the
condition is false, then any lines between the conditional
directive and the #else or #elif (if any) are ignored. If there is
no #else, then the lines between the conditional and the #endif are
ignored.
3 – #define
The #define preprocessor directive has the form:
#define identifier token-string
The preprocessor substitutes the token string everywhere in the
program that it finds the identifier except within comments,
character constants, or string constants.
Macro replacements are defined in a #define directive of the
following form:
#define name([parm1[,parm2,...]]) token-string
Within the program, all macro references that have the following
form are replaced by the token string. The arguments in the macro
reference replace the corresponding parameters in the token string.
name([arg1[,arg2,...]])
4 – #dictionary
The #dictionary directive is retained for compatibility with VAX C
and is supported only when running the VSI C compiler in VAX C mode
(/STANDARD=VAXC). See also the ANSI C equivalent #pragma
dictionary directive.
The #dictionary directive extracts Common Data Dictionary (CDD)
definitions from the specified dictionary. These definitions are
then translated into VSI C and included in the program.
The #dictionary directive has the following form:
#dictionary "cdd_path"
The cdd_path is a character string that gives the path name of the
CDD record. It can also be a macro that resolves to such a
character string.
5 – #error
The #error directive issues an optional diagnostic message, and
ends compilation. This directive has the following form:
#error [message] <newline>
6 – #include
The #include directive instructs the preprocessor to insert the
contents of the specified file or module into the program. An
#include directive can have one of three forms:
#include "filespec"
#include <filespec>
#include module-name
The first two forms are ANSI-compliant methods of file inclusion
and are therefore more portable. In these forms, .h is the default
file type, unless the compiler is instructed to supply no default
type (that is, a type of just ".") by the
/ASSUME=NOHEADER_TYPE_DEFAULT qualifier.
The third form is specific to OpenVMS systems for specifying the
inclusion of a module from a text library, and is not generally
needed or recommended because the ANSI forms also cause the text
libraries to be searched.
For the order of search, see /INCLUDE_DIRECTORY.
There is no defined limit to the nesting level of #include files
and modules.
7 – #line
The #line directive applies a specified line number and optional
file specification to the next line of source text. This can be
useful for diagnostic messages. The #line directive has the
following forms:
#line integer-constant <newline>
#line integer-constant "filename" <newline>
#line pp-tokens <newline>
In the first two forms, the compiler gives the line following a
#line directive the number specified by the integer constant. The
optional filename in quotation marks indicates the name of the
source file that the compiler will provide in its diagnostic
messages. If the filename is omitted, the file name used is the
name of the current source file or the last filename specified in a
previous #line directive.
In the third form, macros in the #line directive are expanded
before it is interpreted. This allows a macro call to expand into
the integer-constant, filename, or both. The resulting #line
directive must match one of the other two forms, and is then
processed as appropriate.
8 – #module
The #module directive is retained for compatibility with VAX C and
is supported only when running the VSI C compiler in VAX C mode
(/STANDARD=VAXC). See also the ANSI C equivalent #pragma module
directive.
The #module directive passes information about an object module to
the compiler.
The #module directive can have one of the following forms:
#module identifier identifier
#module identifier string
The first argument of the directive is an VSI C identifier or macro
that resolves to an identifier. It gives the system-recognized
(for example, internally recognized by the debugger and the
librarian) name of the module; the object file name remains the
same. The second argument specifies the optional identification
that appears on listings. This may be either a VAX C identifier, a
character-string constant with no more than 31 characters, or a
macro that resolves to one of these.
There can be only one #module directive per compilation. It can
appear anywhere before the C language text.
9 – #pragma
The #pragma preprocessor directive performs compiler-specific tasks
as designated by each implementation of the C language.
All pragmas have a <pragma-name>_m version, which makes the pragma
subject to macro replacement. For example, #pragma assert is not
subject to macro expansion, but #pragma assert_m is.
All pragmas also have a <pragma-name>_nm version, which prevents
macro expansion. For example, #pragma inline is subject to macro
expansion, but #pragma inline_nm is not.
There is also a _Pragma operator (C99 Standard), which destringizes
its string literal argument, effectively allowing #pragma
directives to be produced by macro expansion. When specified using
this operator, the tokens of the pragma, which appear together
within a single string literal in this form, are not macro
expanded, even if they have an "_m" suffix. But macro expansion
can be accomplished if desired by using the stringization operator
(#) to form the string.
The _Pragma operator has the following syntax:
_Pragma ( string-literal )
VSI C for OpenVMS Systems supports the following #pragma
directives:
#pragma assert[_m|_nm]
Lets you specify assertions that the compiler can make about a
program to generate more efficient code.
The #pragma assert directive is never needed to make a program
execute correctly, however if a #pragma assert is specified,
the assertions must be valid or the program might behave
incorrectly.
Syntax:
#pragma assert func_attrs(identifier-list)function-assertions
#pragma assert global_status_variable(variable-list)
#pragma assert non_zero(constant-expression) string-literal
Descriptions follow.
The #pragma assert func_attrs directive:
The identifier-list is a list of function identifiers about
which the compiler can make assertions. If more than one
identifier is specified, separate them by commas.
The function-assertions specify the assertions for the compiler
to make about the functions. Specify one or more of the
following, separating multiple assertions with whitespace:
noreturn
The compiler can assert that any call to the routine will
never return.
nocalls_back
The compiler can assert that no routine in the source
module will be called before control is returned from this
function.
nostate
The compiler can assert that the value returned by the
function and any side-effects the function might have are
determined only by the function's arguments. If a
function is marked as having both noeffects and nostate,
the compiler can eliminate redundant calls to the
function.
noeffects
The compiler can assert that any call to this function
will have no effect except to set the return value of the
function. If the compiler determines that the return
value from a function call is never used, it can remove
the call.
file_scope_vars(option)
The compiler can make assertions about how a function will
access variables declared at file scope (with either
internal or external linkage).
The file_scope_vars option is one of the following:
o none - The function will not read nor write to any
file-scope variables except those whose type is
volatile or those listed in a #pragma assert
global_status_variable.
o noreads - The function will not read any file-scope
variables except those whose type is volatile or those
listed in a #pragma assert global_status_variable.
o nowrites - The function will not write to any
file-scope variables except those whose type is
volatile or those listed in a #pragma assert
global_status_variable.
format (<style>, <format-index>, <first-to-check-index>)
Asserts to the compiler that this function takes printf-
or scanf-style arguments to be type-checked against a
format string. Specify the parameters as follows:
o <style> -- PRINTF or SCANF.
This determines how the format string is interpreted.
o <format-index> -- {1|2|3|...}
This specifies which argument is the format-string
argument (starting from 1).
o <first-to-check-index> -- {0|1|2|...}
This is the number of the first argument to check
against the format string. For functions where the
arguments are not available to be checked (such as
vprintf), specify the third parameter as 0. In this
case, the compiler only checks the format string for
consistency.
The #pragma assert global_status_variable directive:
Use the #pragma assert global_status_variable(variable-list)
form of the pragma to specify variables that are to be
considered global status variables, which are exempt from any
assertions given to functions by #pragma assert func_attrs
file_scope_vars directives.
The variable-list is a list of variables.
The #pragma assert non_zero directive:
When the compiler encounters this directive, it evaluates the
constant-expression. If the expression is zero, the compiler
generates a message that contains both the specified
string-literal and the compile-time constant-expression. For
example:
#pragma assert non_zero(sizeof(a) == 12) "a is the wrong size"
In this example, if the compiler determines that the sizeof a
is not 12, the following diagnostic message is output:
CC-W-ASSERTFAIL, The assertion "(sizeof(a) == 12)" was not
true. a is the wrong size.
Unlike the #pragma assert options func_attrs and
global_status_variable, #pragma assert non_zero can appear
either inside or outside a function body. When used inside a
function body, the pragma can appear wherever a statement can
appear, but the pragma is not treated as a statement. When
used outside a function body, the pragma can appear anywhere a
declaration can appear, but the pragma is not treated as a
declaration.
Because macro replacement is not performed on #pragma assert,
you might need to use the #pragma assert_m directive to obtain
the results you want. Consider the following program that
verifies both the size of a struct and the offset of one of its
elements:
#include <stddef.h>
typedef struct {
int a;
int b;
} s;
#pragma assert non_zero(sizeof(s) == 8) "sizeof assert failed"
#pragma assert_m non_zero(offsetof(s,b) == 4) "offsetof assert
failed"
Because offsetof is a macro, the second pragma must be #pragma
assert_m so that offsetof will expand correctly.
#pragma builtins[_m|_nm]
Enables the VSI C built-in functions that directly access
processor instructions.
The #pragma builtins directive is provided for VAX C
compatibility.
VSI C implements #pragma builtins by including the <builtins.h>
header file, and is equivalent to #include <builtins.h> on
OpenVMS systems.
This header file contains prototype declarations for the
built-in functions that allow them to be used properly. By
contrast, VAX C implemented this pragma with special-case code
within the compiler, which also supported a #pragma nobuiltins
preprocessor directive to turn off the special processing.
Because declarations cannot be "undeclared", VSI C does not
support #pragma nobuiltins. Furthermore, the names of all the
built-in functions use a naming convention defined by ANSI C to
be in a namespace reserved to the C language implementation.
#pragma dictionary[_m|_nm]
Allows you to extract CDD data definitions and include these
definitions in your program.
The ANSI C compliant #pragma dictionary directive is equivalent
to the VAX C compatible #dictionary directive, but is supported
in all compiler modes. (The #dictionary directive is retained
for compatibility and is supported only when compiling with the
/STANDARD=VAXC qualifier.)
Syntax:
#pragma dictionary "cdd_path" [null_terminate]
[name(structure_name)] [text1_to_array | text1_to_char]
The cdd_path is a character string that gives the path name of
the CDD record. It can also be a macro that resolves to such a
character string.
The optional null_terminate keyword can be used to specify that
all string data types should be null-terminated.
The optional name() can be used to supply an alternate tag name
or a declarator, struct_name for the outer level of a CDD
structure.
The optional text1_to_char keyword forces the CDD type "text"
to be translated to char, rather than "array of char" if the
size is 1. This is the default if null_terminate is not
specified.
The optional text1_to_array keyword forces the CDD type "text"
to be translated to type "array of char" even when the size
is 1. This is the default when null_terminate is specified.
#pragma environment[_m|_nm]
Sets, saves, or restores the states of context pragmas. This
directive protects include files from contexts set by
encompassing programs, and protects encompassing programs from
contexts that could be set in header files that they include.
The #pragma environment directive affects the following
pragmas:
o #pragma extern_model
o #pragma extern_prefix
o #pragma member_alignment
o #pragma message
o #pragma names
o #pragma pointer_size
o #pragma required_pointer_size
Syntax:
#pragma environment command_line
#pragma environment header_defaults
#pragma environment restore
#pragma environment save
command_line
Sets, as specified on the command line, the states of all
the context pragmas. You can use this pragma to protect
header files from environment pragmas that take effect
before the header file is included.
header_defaults
Sets the states of all the context pragmas to their
default values. This is almost equivalent to the
situation in which a program with no command-line options
and no pragmas is compiled, except that this pragma sets
the pragma message state to #pragma nostandard, as is
appropriate for header files.
save
Saves the current state of every pragma that has an
associated context.
restore
Restores the current state of every pragma that has an
associated context.
#pragma extern_model[_m|_nm]
Controls the compiler's interpretation of objects that have
external linkage. This pragma lets you choose the global
symbol model to be used for externs.
Syntax:
#pragma extern_model common_block [attr[,attr]...]
#pragma extern_model relaxed_refdef [attr[,attr]...]
#pragma extern_model strict_refdef "name" [attr[,attr]...]
#pragma extern_model strict_refdef
#pragma extern_model globalvalue
#pragma extern_model save
#pragma extern_model restore
The default model on VSI C is #pragma relaxed_refdef noshr.
This is different from the model used by VAX C, which is common
block, shr.
The [attr[,attr]...] are optional psect attribute
specifications chosen from the following (at most one from each
line):
o gbl lcl (Not allowed with relaxed_refdef)
o shr noshr
o wrt nowrt
o pic nopic (Not meaningful for Alpha)
o ovr con
o rel abs
o exe noexe
o vec novec
o noreorder (named strict_refdef only)
o natalgn (named strict_refdef only)
o 0 byte 1 word 2 long 3 quad 4 octa 5 6 7 8 9 10 11 12 13 14
15 16 page
See the HP C User's Guide for more information on the #pragma
extern_model directive.
#pragma extern_prefix[_m|_nm]
Controls the compiler's synthesis of external names, which the
linker uses to resolve external name requests.
When you specify #pragma extern_prefix with a string argument,
the compiler prepends the string to all external names
produced by the declarations that follow the pragma
specification.
This pragma is useful for creating libraries where the
facility code can be attached to the external names in the
library.
Syntax:
#pragma extern_prefix "string" [(id[,id]...)]
#pragma extern_prefix {NOCRTL|RESTORE_CRTL} (id[,id]...)
#pragma extern_prefix save
#pragma extern_prefix restore
Where "string" prepends the quoted string to external names in
the declarations that follow the pragma specification.
You can also specify an extern prefix for specific identifiers
using the optional list [(<emphasis>(id)[,<emphasis>(id)]...)].
The NOCRTL and RESTORE_CRTL keywords control whether or not the
compiler applies its default RTL prefixing to the names
specified in the id-list, required for this form of the pragma.
The effect of NOCRTL is like that of the EXCEPT=keyword of the
/PREFIX_LIBRARY_ENTRIES command-line qualifier. The effect of
RESTORE_CRTL is to undo the effect of a #pragma extern_prefix
NOCRTL or a /PREFIX=EXCEPT= on the command line.
The save and restore keywords can be used to save the current
pragma prefix string and to restore the previously saved pragma
prefix string, respectively.
The default external prefix, when none has been specified by a
pragma, is the null string.
#pragma function[_m|_nm]
Specifies that calls to the specified functions are not
intrinsic but are, in fact, function calls. This pragma has
the opposite effect of #pragma intrinsic.
Syntax:
#pragma function[_m|_nm] (function1[, function2, ...])
#pragma include_directory[_m|_nm]
The effect of each #pragma include_directory is as if its
string argument (including the quotes) were appended to the
list of places to search that is given its initial value by the
/INCLUDE_DIRECTORY qualifier, except that an empty string is
not permitted in the pragma form.
Syntax:
#pragma include_directory <string-literal>
This pragma is intended to ease DCL command-line length
limitations when porting applications from POSIX-like
environments built with makefiles containing long lists of -I
options specifying directories to search for headers. Just as
long lists of macro definitions specified by the /DEFINE
qualifier can be converted to #define directives in a source
file, long lists of places to search specified by the
/INCLUDE_DIRECTORY qualifier can be converted to #pragma
include_directory directives in a source file.
Note that the places to search, as described in the help text
for the /INCLUDE_DIRECTORY qualifier, include the use of
POSIX-style pathnames, for example "/usr/base". This form can
be very useful when compiling code that contains POSIX-style
relative pathnames in #include directives. For example,
#include <subdir/foo.h> can be combined with a place to search
such as "/usr/base" to form "/usr/base/subdir/foo.h", which
will be translated to the filespec "USR:[BASE.SUBDIR]FOO.H"
This pragma can appear only in the main source file or in the
first file specified on the /FIRST_INCLUDE qualifier. Also, it
must appear before any #include directives.
#pragma [no]inline[_m|_nm]
Expands function calls inline. The function call is replaced
with the function code itself.
Syntax:
#pragma inline (id,...)
#pragma noinline (id,...)
If a function is named in an inline directive, calls to that
function will be expanded as inline code, if possible.
If a function is named in a noinline directive, calls to that
function will not be expanded as inline code.
If a function is named in both an inline and a noinline
directive, an error message is issued.
For calls to functions named in neither an inline nor a
noinline directive, DEC C expands the function as inline code
whenever appropriate as determined by a platform-specific
algorithm.
#pragma intrinsic[_m|_nm]
Specifies that calls to the specified functions are intrinsic
(that is, handled internally by the compiler, allowing it to
generate inline code, move or eliminate calls, or do various
other optimizations). This pragma is only valid for functions
that are known to the compiler.
Syntax:
#pragma intrinsic (function1[, function2, ...])
#pragma linkage[_m|_nm]
Specifies special linkage types for function calls. This
pragma is used with the #pragma use_linkage directive, which
associates a previously defined special linkage with a
function.
Syntax:
#pragma linkage linkage-name = (characteristics)
#pragma linkage_ia64 linkage-name = (characteristics)
On I64 systems, these two formats behave differently:
o The #pragma linkage_ia64 format requires I64 register names
be specified.
o The #pragma linkage format requires Alpha register names be
specified, which are automatically mapped, where possible,
to specific I64 registers.
The two formats are further described after the description of
the characteristics.
The characteristics specify information about where parameters
will be passed, where the results of the function are to be
received, and what registers are modified by the function call.
Specify these characteristics as a parenthesized list of items
of the following forms:
parameters (register-list)
result (simple-register-list)
preserved (simple-register-list)
nopreserve (simple-register-list)
notused (simple-register-list)
notneeded (ai, lp)
standard_linkage
You can supply the option keywords in any order.
Description of Options:
simple-register-list
A comma-separated list of register names, either Rn or Fn.
Example:
nopreserve(F5, F6)
For the #pragma linkage format, valid registers for the
preserved, nopreserve, and notused options include
general-purpose registers R0 through R30, and
floating-point registers F0 through F30.
Valid registers for the result and parameters options
include general-purpose registers R0 through R25, and
floating-point registers F0 through F30.
For the #pragma linkage_ia64 format, see below for an
explanation of register usage.
register-list
Similar to a simple-register-list except that it can
contain parenthesized sublists. Use the register-list to
describe arguments and function result types that are
structs, where each member of the struct is passed in a
single register. Example:
parameters(R5, (F5, F6))
parameters
Use this option to pass arguments to the parameters of a
routine in specific registers.
result
Use this option to specify the register to be used to
return the value for the function. If a function has a
return type of void, do not specify the result option as
part of the linkage.
preserved
A preserved register contains the same value after a call
to the function as it did before the call.
nopreserve
A nopreserve register does not necessarily contain the
same value after a call to the function as it did before
the call.
notused
A notused register is not used in any way by the called
function.
notneeded
Indicates that certain items are not needed by the
routines using this linkage. Valid options are:
AI -- Specifies that the Argument Information
register (R25) does not need to be set up when
calling the specified functions.
LP -- Specifies that the Linkage Pointer register
does not need to be set up when calling the specified
functions. Note that for I64 systems, there is no
linkage pointer, so this setting is accepted but does
not change the behavior of the pragma.
standard_linkage
Tells the compiler to use the standard linkage appropriate
to the target platform. This can be useful to confine
conditional compilation to the pragmas that define
linkages, without requiring the corresponding #pragma
use_linkage directives to be conditionally compiled as
well.
If the standard_linkage keyword is specified, it must be
the only option in the parenthesized list following the
linkage name. For example:
#pragma linkage special1 = (standard_linkage)
If the standard_linkage keyword is not specified, you can
supply the parameters, result, preserved, nopreserve, and
notused options in any order, separated by commas.
Description of the two formats of this pragma:
The #pragma linkage_ia64 format of this preprocessor directive
requires register names to be specified in terms of an OpenVMS
I64 system. The register names are never mapped to a different
architecture. This form of the pragma always produces an error
if encountered on a different architecture.
For this format of the pragma, valid registers for the
preserved, nopreserve, notused, parameters, and result options
are:
o Integer registers R3 through R12 and R19 through R31
o Floating-point registers F2 through F31
In addition, the parameters and result options also permit
integer registers R32 through R39 to be specified, according to
the following convention. On IA64, the first eight integer
input/output slots are allocated to stacked registers, and thus
the calling routine refers to them using different names than
the called routine. The convention for naming these registers
in either the parameters or result option of a #pragma
linkage_ia64 directive is always to use the hardware names as
they would be used within the called routine: R32 through R39.
The compiler automatically compensates for the fact that within
the calling routine these same registers are designated using
different hardware names.
The #pragma linkage format of this preprocessor directive
accepts Alpha register names and conventions and automatically
maps them, where possible, to specific I64 registers. So
whenever VSI C for I64 encounters a #pragma linkage directive,
it attempts to map the Alpha registers specified in the linkage
to corresponding I64 registers, and emits a SHOWMAPLINKAGE
informational message showing the I64 specific form of the
directive, #pragma linkage_ia64, with the I64 register names
that replaced the Alpha register names. The SHOWMAPLINKAGE
message is suppressed under the #pragma nostandard directive,
normally used within system header files.
Code compiled on I64 systems that deliberately relies on the
register mapping performed by #pragma linkage should either
ignore the SHOWMAPLINKAGE informational, or disable it.
The following shows the mapping that VSI C applies to the Alpha
integer register names used in #pragma linkage format
directives when they are encountered on an I64 system. Note
that the six standard parameter registers on Alpha (R16-R21)
are mapped to the first six (of eight) standard parameter
registers on I64 systems, which happen to be stacked registers:
Integer Register Mapping:
Alpha -> I64 Alpha -> I64
R0 -> R8 R16 -> R32 *
R1 -> R9 R17 -> R33 *
R2 -> R28 R18 -> R34 *
R3 -> R3 R19 -> R35 *
R4 -> R4 R20 -> R36 *
R5 -> R5 R21 -> R37 *
R6 -> R6 R22 -> R22
R7 -> R7 R23 -> R23
R8 -> R26 R24 -> R24
R9 -> R27 R25 -> R25
R10 ->R10 R26 - no mapping
R11 ->R11 R27 - no mapping
R12 ->R30 R28 - no mapping
R13 ->R31 R29 -> R29
R14 ->R20 R30 -> R12
R15 ->R21 R31 -> R0
* In parameters or result; else ignored
The following shows the mapping that VSI C applies to the Alpha
floating-point register names used in #pragma linkage
directives when they are encountered on an I64 system:
Floating-Point Register Mapping:
Alpha -> I64 Alpha -> I64
F0 -> F8 F16 -> F8
F1 -> F9 F17 -> F9
F2 -> F2 F18 -> F10
F3 -> F3 F19 -> F11
F4 -> F4 F20 -> F12
F5 -> F5 F21 -> F13
F6 -> F16 F22 -> F22
F7 -> F17 F23 -> F23
F8 -> F18 F24 -> F24
F9 -> F19 F25 -> F25
F10 ->F6 F26 - F26
F11 ->F7 F27 - F27
F12 ->F20 F28 - F28
F13 ->F21 F29 -> F29
F14 ->F14 F30 -> F30
F15 ->F15
Mapping Diagnostics:
In some cases, the HP C compiler on Alpha systems silently
ignores linkage registers if, for example, a standard parameter
register like R16 is specified in a preserved option. When you
compile on an I64 system, this situation emits an MAPREGIGNORED
informational message, and the SHOWMAPLINKAGE output might not
be correct. If there is no valid mapping to I64 registers, the
NOMAPPOSSIBLE error message is output. There are two special
situations that can arise when floating-point registers are
specified in a linkage:
o Only IEEE-format values are passed in floating-point
registers under the OpenVMS Calling Standard for I64: VAX
format values are passed in integer registers. Therefore,
a compilation that specifies /FLOAT=D_FLOAT or
/FLOAT=G_FLOAT produces an error for any linkage that
specifies floating-point registers. Note that this
includes use in options that do not involve passing values,
such as the preserved and notused options.
o The mapping of floating-point registers is many-to-one in
two cases:
- Alpha registers F0 and F16 both map to I64 register F8
- Alpha F1 and F17 both map to I64 register F9.
A valid Alpha linkage may well specify uses for both F0 and
F16, and/or both F1 and F17. Such a linkage cannot be
mapped on an I64 system. But because of the way this
situation is detected, the MULTILINKREG warning message
that is produced can only identify the second occurrence of
an Alpha register that got mapped to the same I64 register
as some previous Alpha register. The actual pair of Alpha
registers in the source is not identified, and so the
message can be confusing. For example, an option like
preserved(F1,F17) gets a MULTILINKREG diagnostic saying
that F17 was specified more than once.
#pragma [no]member_alignment[_m|_nm]
Tells the compiler to align structure members on the next
boundary appropriate to the type of the member rather than the
next byte. For example, a long variable is aligned on the next
longword boundary; a short variable on the next word boundary.
Syntax:
#pragma nomember_alignment [base_alignment]
#pragma member_alignment [save | restore]
The optional base_alignment parameter can be used with #pragma
nomember_alignment to specify the base alignment of the
structure. Use one of the following keywords to specify the
base_alignment:
o BYTE (1 byte)
o WORD (2 bytes)
o LONGWORD (4 bytes)
o QUADWORD (8 bytes)
o OCTAWORD (16 bytes)
The optional save and restore keywords can be used to save the
current state of the member_alignment and to restore the
previous state, respectively. This feature is necessary for
writing header files that require member_alignment or
nomember_alignment, or that require inclusion in a
member_alignment that is already set.
#pragma message[_m|_nm]
Controls the issuance of individual diagnostic messages or
groups of messages. Use of this pragma overrides any
command-line options that may affect the issuance of messages.
Syntax:
#pragma message option1 message-list
#pragma message option2
#pragma message (quoted-string)
where option1 is:
disable Suppresses the issuance of the indicated
messages.
Only messages of severity Warning (W) or
Information (I) can be disabled. If the
message has severity of Error (E) or
Fatal (F), it is issued regardless of
any attempt to disable it.
enable Enables the issuance of the indicated
messages.
emit_once Emits the specified messages only once
per compilation.
emit_always Emits the specified messages at every
occurrence of the condition.
error Sets the severity of each message in the
message-list to Error.
fatal Sets the severity of each message on the
message-list to Fatal.
informational Sets the severity of each message in the
message-list to Informational.
warning Sets the severity of each message in the
message-list to Warning.
The message-list can be any one of the following:
o A single message identifier (within parentheses or not).
o A single message-group name (within parentheses or not).
Message-group names are:
ALL All the messages in the compiler
ALIGNMENT Messages about unusual or inefficient
data alignment.
C_TO_CXX Messages reporting the use of C features
that would be invalid or have a
different meaning if compiled by a C++
compiler.
CDD Messages about CDD (Common Data
Dictionary) support.
CHECK Messages reporting code or practices
that, although correct and perhaps
portable, are sometimes considered
ill-advised because they can be
confusing or fragile to maintain. For
example, assignment as the test
expression in an "if" statement.
NOTE: The check group gets defined by
enabling level5 messages.
DEFUNCT Messages reporting the use of obsolete
features: ones that were commonly
accepted by early C compilers but were
subsequently removed from the language.
NEWC99 Messages reporting the use of the new
C99 Standard features.
NOANSI Messages reporting the use of non-ANSI
Standard features. The NOANSI message
group is a synonym for NOC89. Also see
message groups NEWC99, NOC89, NOc99.
NOC89 Messages reporting the use of non-C89
Standard features.
NOC99 Messages reporting the use of non-C99
Standard features.
OBSOLESCENT Messages reporting the use of features
that are valid in ANSI Standard C, but
which were identified in the standard as
being obsolescent and likely to be
removed from the language in a future
version of the standard.
OVERFLOW Messages that report assignments and/or
casts that can cause overflow or other
loss of data significance.
PERFORMANCE Messages reporting code that might
result in poor run-time performance.
PORTABLE Messages reporting the use of language
extensions or other constructs that
might not be portable to other compilers
or platforms.
PREPROCESSOR Messages reporting questionable or
non-portable use of preprocessing
constructs.
QUESTCODE Messages reporting questionable coding
practices. Similar to the check group,
but messages in this group are more
likely to indicate a programming error
rather than just a non-robust style.
Enabling the QUESTCODE group provides
lint-like checking.
RETURNCHECKS Messages related to function return
values.
UNINIT Messages related to using uninitialized
variables.
UNUSED Messages reporting expressions,
declarations, header files, CDD records,
static functions, and code paths that
are not used.
Note, however, that unlike any other
messages, these messages must be enabled
on the command line
(/WARNINGS=ENABLE=UNUSED) to be
effective.
o A single message-level name (within parentheses or not).
Note: There is a core of very important compiler messages
that are enabled by default, regardless of anything
specified with /WARNINGS or #pragma message. Referred to as
message level 0, it includes all messages issued in header
files, and comprises what is known as the nostandard group.
All other message levels add additional messages to this
core of enabled messages.
You cannot disable level 0. However, you can disable
individual messages in level 0 that are not errors or
fatals.
Message-level names are:
LEVEL1 Important messages. These are less
important than level 0, because messages
in this group are not displayed if #pragma
nostandard is active.
LEVEL2 Moderately important messages. This level
is used to introduce new messages that
will be output in the DIGITAL UNIX V4.0
release. LEVEL2 is the default for
DIGITAL UNIX and Tru64 UNIX platforms.
LEVEL3 Less important messages. In general,
these are the messages output by default
in DEC C Version 5.5 for OpenVMS Systems.
LEVEL3 is the default message level for
VSI C for OpenVMS systems.
LEVEL4 Useful check/portable messages.
LEVEL5 Not so useful check/portable messages.
LEVEL6 All messages in LEVEL5 plus additional
"noisy" messages.
Enabling a level also enables all the messages in the levels
below it. So enabling LEVEL3 messages also enables messages
in LEVEL2 and LEVEL1.
Disabling a level also disables all the messages in the
levels above it. So disabling LEVEL4 messages also disables
messages in LEVEL5 and LEVEL6.
o A comma-separated list of message identifiers, group names,
and messages levels, freely mixed, enclosed in parentheses.
option2 is:
save -- saves the current state of which messages are
enabled and disabled.
restore -- restores the previous state of which messages
are enabled and disabled.
The save and restore options are useful primarily within header
files.
The #pragma message (quoted-string) form outputs the
quoted-string as a compiler message. This form of the pragma is
subject to macro replacement. For example, the following is
valid:
#pragma message ("Compiling file " __FILE__)
#pragma module[_m|_nm]
The ANSI C compliant #pragma module directive is equivalent to
the VAX C compatible #module directive, but is supported in all
compiler modes. (The #module directive is retained for
compatibility and is supported only when compiling with the
/STANDARD=VAXC qualifier.) The #pragma module directive is
specific to VSI C for OpenVMS Systems and is not portable.
Use the #pragma module directive to change the
system-recognized module name and version number. You can find
the module name and version number in the compiler listing file
and the linker load map.
Syntax:
#pragma module identifier identifier
#pragma module identifier string
The first parameter must be a valid VSI C identifier. It
specifies the module name to be used by the linker. The second
parameter specifies the optional identification that appears on
listings and in the object file. It must be either a valid VSI
C identifier of 31 characters or less, or a character-string
constant of 31 characters or less.
Only one #pragma module directive can be processed per
compilation unit, and that directive must appear before any C
language text. The #pragma module directive can follow other
directives, such as #define, but it must precede any function
definitions or external data definitions.
#pragma names[_m|_nm]
Provides the same kinds of control over the mapping of external
identifiers' object-module symbols as does the /NAMES
command-line qualifier, and it uses the same keywords. But as
a pragma, the controls can be applied selectively to regions of
declarations.
This pragma should only be used in header files and is intended
for use by developers who supply libraries and/or header files
to their customers.
The pragma has a save/restore stack that is also managed by
#pragma environment, and so it is well-suited for use in header
files. The effect of #pragma environment header_defaults is to
set NAMES to "uppercase,truncated", which is the compiler
default.
Syntax:
#pragma names <stack-option>
#pragma names <case-option>
#pragma names <length-option>
Where
<stack-option> is one of:
o save - save the current names state
o restore - restore a saved names state
<case-option> is one of:
o uppercase - uppercase external names
o as_is - do not change case
<length-option> is one of:
o truncated - truncate at 31 characters
o shortened - shorten to 31 using CRC
#pragma optimize[_m|_nm]
Sets the optimization characteristics of function definitions
that follow the directive. It allows optimization-control
options that are normally set on the command line for the
entire compilation to be specified in the source file for
individual functions.
Syntax:
#pragma optimize <settings>
#pragma optimize save
#pragma optimize restore
#pragma optimize command_line
Where <settings> is any combination of the following:
o <level settings>
Set the optimization level. Specify as:
level=n
Where n is an integer from 0 to 5.
o <unroll settings>
Control loop unrolling. Specify as:
unroll=n
Where n is a nonnegative integer.
o <ansi-alias settings>
Control ansi-alias assumptions. Specify one of the following:
ansi_alias=on
ansi_alias=off
o <intrinsic settings>
Control recognition of intrinsics. Specify one of the
following:
intrinsics=on
intrinsics=off
Use the save, restore, and command_line keywords as follows:
o save -- Saves the current pointer size
o restore -- Restores the current pointer size to its last
saved state
o command_line -- Sets the optimization settings to what was
specified on the command line
Example:
#pragma optimize level=5 unroll=6
Usage Notes:
o If the level=0 clause is present, it must be the only
clause present.
o The #pragma optimize directive must appear at file scope,
outside any function body.
o The #pragma environment save and restore operations include
the optimization state.
o The #pragma environment command_line directive resets the
optimization state to that specified on the command line.
o If #pragma optimize does not specify a setting for one of
the optimization states, that state remains unchanged.
o When a function definition is encountered, it is compiled
using the optimization settings that are current at that
point in the source.
o When a function is compiled under level=0, the compiler
will not inline that function. In general, when functions
are inlined, the inlined code is optimized using the
optimization controls in effect at the call site instead of
using the optimization controls specified for the function
being inlined.
o When the OpenVMS command line specifies /NOOPT (or
/OPTIMIZE=LEVEL=0), the #pragma optimize directive has no
effect (except that its arguments are still validated).
#pragma pack[_m|_nm]
Specifies the byte boundary for packing members of C
structures.
Syntax:
#pragma pack [n]
The n specifies the new alignment restriction in bytes:
1 - align to byte
2 - align to word
4 - align to longword
8 - align to quadword
16 - align to octaword
A structure member is aligned to either the alignment specified
by #pragma pack or the alignment determined by the size of the
structure member, whichever is smaller. For example, a short
variable in a structure gets byte-aligned if #pragma pack 1 is
specified. If #pragma pack 2, 4, or 8 is specified, the short
variable in the structure gets aligned to word.
When #pragma pack is specified without a value or with a value
of 0, packing reverts to that specified by the
/[NO]MEMBER_ALIGNMENT qualifier setting (either explicitly
specified or by default) on the command line. Note that when
specifying #pragma pack without a value, you must use
parentheses: #pragma pack ().
#pragma pointer_size[_m|_nm]
Controls whether pointers are 32-bit pointers or 64-bit
pointers.
Syntax:
#pragma pointer_size keyword
Where keyword is one of the following:
o short -- 32-bit pointer
o long -- 64-bit pointer
o system_default -- 32-bit pointers on OpenVMS systems;
64-bit pointers on Tru64 UNIX systems
o save -- Saves the current pointer size
o restore -- Restores the current pointer size to its last
saved state
This directive is enabled only when the /POINTER_SIZE command-line
qualifier is specified. Otherwise, #pragma pointer_size has the
same effect as #pragma required_pointer_size.
#pragma required_pointer_size[_m|_nm]
Intended for use by developers of header files to control
pointer size within header files.
Syntax:
#pragma required_pointer_size keyword
Where keyword is one of the following:
o short -- 32-bit pointer
o long -- 64-bit pointer
o system_default -- 32-bit pointers on OpenVMS systems;
64-bit pointers on Tru64 UNIX systems
o save -- Saves the current pointer size
o restore -- Restores the current pointer size to its last
saved state
This directive is always enabled, even if the /POINTER_SIZE
command-line qualifier is omitted. Otherwise, #pragma
required_pointer_size has the same effect as #pragma pointer_size.
#pragma [no]standard[_m|_nm]
Directs the compiler to define regions of source code where
portability diagnostics are not to be issued.
Use #pragma nostandard to suppress diagnostics about non-ANSI C
extensions, regardless of the /STANDARD qualifier specified,
until a #pragma standard directive is encountered.
Use #pragma standard to reinstate the setting of the /STANDARD
qualifier that was in effect before before the last #pragma
nostandard was encountered.
Every #pragma standard directive must be preceded by a
corresponding #pragma nostandard directive.
Note that this pragma does not change the current mode of the
compiler or enable any extensions not already supported in that
mode.
#pragma unroll[_m|_nm]
Directs the compiler to unroll the for loop that follows it by
the number of times specified in the unroll_factor argument.
The #pragma unroll directive must be followed by a for
statement.
Syntax:
#pragma unroll (unroll_factor)
The unroll_factor is an integer constant in the range 0 to 255.
If a value of 0 is specified, the compiler ignores the
directive and determines the number of times to unroll the loop
in its normal way. A value of 1 prevents the loop from being
unrolled. The directive applies only to the for loop that
follows it, not to any subsequent for loops.
#pragma use_linkage[_m|_nm]
Associates a special linkage, defined by the #pragma linkage
directive, with the specified functions.
Syntax:
#pragma use_linkage linkage-name (routine1, routine2, ...)
The linkage-name is the name of a linkage previously defined by
the #pragma linkage directive.
The parenthesized list contains the names of functions you want
to associated with the named linkage.
The list can also contain typedef names of function type, in
which case functions or pointers to functions declared using
that type will have the specified linkage.
10 – #undef
The #undef directive cancels a previously defined macro
replacement. Any other macro replacements that occurred before the
#undef directive remain.
The #undef directive has the following syntax:
#undef identifier