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