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Info file cpp.info, produced by Makeinfo, -*- Text -*- from input file cpp.texinfo. This file documents the GNU C Preprocessor. Copyright (C) 1987, 1989 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions. File: cpp.info, Node: Self-Reference, Next: Argument Prescan, Prev: Side Effects, Up: Macro Pitfalls Self-Referential Macros ....................... A "self-referential" macro is one whose name appears in its definition. A special feature of ANSI Standard C is that the self-reference is not considered a macro call. It is passed into the preprocessor output unchanged. Let's consider an example: #define foo (4 + foo) where `foo' is also a variable in your program. Following the ordinary rules, each reference to `foo' will expand into `(4 + foo)'; then this will be rescanned and will expand into `(4 + (4 + foo))'; and so on until it causes a fatal error (memory full) in the preprocessor. However, the special rule about self-reference cuts this process short after one step, at `(4 + foo)'. Therefore, this macro definition has the possibly useful effect of causing the program to add 4 to the value of `foo' wherever `foo' is referred to. In most cases, it is a bad idea to take advantage of this feature. A person reading the program who sees that `foo' is a variable will not expect that it is a macro as well. The reader will come across the identifier `foo' in the program and think its value should be that of the variable `foo', whereas in fact the value is four greater. The special rule for self-reference applies also to "indirect" self-reference. This is the case where a macro X expands to use a macro `y', and `y''s expansion refers to the macro `x'. The resulting reference to `x' comes indirectly from the expansion of `x', so it is a self-reference and is not further expanded. Thus, after #define x (4 + y) #define y (2 * x) `x' would expand into `(4 + (2 * x))'. Clear? But suppose `y' is used elsewhere, not from the definition of `x'. Then the use of `x' in the expansion of `y' is not a self-reference because `x' is not ``in progress''. So it does expand. However, the expansion of `x' contains a reference to `y', and that is an indirect self-reference now because `y' is ``in progress''. The result is that `y' expands to `(2 * (4 + y))'. It is not clear that this behavior would ever be useful, but it is specified by the ANSI C standard, so you need to understand it. File: cpp.info, Node: Argument Prescan, Next: Cascaded Macros, Prev: Self-Reference, Up: Macro Pitfalls Separate Expansion of Macro Arguments ..................................... We have explained that the expansion of a macro, including the substituted actual arguments, is scanned over again for macro calls to be expanded. What really happens is more subtle: first each actual argument text is scanned separately for macro calls. Then the results of this are substituted into the macro body to produce the macro expansion, and the macro expansion is scanned again for macros to expand. The result is that the actual arguments are scanned *twice* to expand macro calls in them. Most of the time, this has no effect. If the actual argument contained any macro calls, they are expanded during the first scan. The result therefore contains no macro calls, so the second scan does not change it. If the actual argument were substituted as given, with no prescan, the single remaining scan would find the same macro calls and produce the same results. You might expect the double scan to change the results when a self-referential macro is used in an actual argument of another macro (*note Self-Reference::.): the self-referential macro would be expanded once in the first scan, and a second time in the second scan. But this is not what happens. The self-references that do not expand in the first scan are marked so that they will not expand in the second scan either. The prescan is not done when an argument is stringified or concatenated. Thus, #define str(s) #s #define foo 4 str (foo) expands to `"foo"'. Once more, prescan has been prevented from having any noticeable effect. More precisely, stringification and concatenation use the argument as written, in un-prescanned form. The same actual argument would be used in prescanned form if it is substituted elsewhere without stringification or concatenation. #define str(s) #s lose(s) #define foo 4 str (foo) expands to `"foo" lose(4)'. You might now ask, ``Why mention the prescan, if it makes no difference? And why not skip it and make the preprocessor faster?'' The answer is that the prescan does make a difference in three special cases: * Nested calls to a macro. * Macros that call other macros that stringify or concatenate. * Macros whose expansions contain unshielded commas. We say that "nested" calls to a macro occur when a macro's actual argument contains a call to that very macro. For example, if `f' is a macro that expects one argument, `f (f (1))' is a nested pair of calls to `f'. The desired expansion is made by expanding `f (1)' and substituting that into the definition of `f'. The prescan causes the expected result to happen. Without the prescan, `f (1)' itself would be substituted as an actual argument, and the inner use of `f' would appear during the main scan as an indirect self-reference and would not be expanded. Here, the prescan cancels an undesirable side effect (in the medical, not computational, sense of the term) of the special rule for self-referential macros. But prescan causes trouble in certain other cases of nested macro calls. Here is an example: #define foo a,b #define bar(x) lose(x) #define lose(x) (1 + (x)) bar(foo) We would like `bar(foo)' to turn into `(1 + (foo))', which would then turn into `(1 + (a,b))'. But instead, `bar(foo)' expands into `lose(a,b)', and you get an error because `lose' requires a single argument. In this case, the problem is easily solved by the same parentheses that ought to be used to prevent misnesting of arithmetic operations: #define foo (a,b) #define bar(x) lose((x)) The problem is more serious when the operands of the macro are not expressions; for example, when they are statements. Then parentheses are unacceptable because they would make for invalid C code: #define foo { int a, b; ... } In GNU C you can shield the commas using the `({...})' construct which turns a compound statement into an expression: #define foo ({ int a, b; ... }) Or you can rewrite the macro definition to avoid such commas: #define foo { int a; int b; ... } There is also one case where prescan is useful. It is possible to use prescan to expand an argument and then stringify it--if you use two levels of macros. Let's add a new macro `xstr' to the example shown above: #define xstr(s) str(s) #define str(s) #s #define foo 4 xstr (foo) This expands into `"4"', not `"foo"'. The reason for the difference is that the argument of `xstr' is expanded at prescan (because `xstr' does not specify stringification or concatenation of the argument). The result of prescan then forms the actual argument for `str'. `str' uses its argument without prescan because it performs stringification; but it cannot prevent or undo the prescanning already done by `xstr'. File: cpp.info, Node: Cascaded Macros, Prev: Argument Prescan, Up: Macro Pitfalls Cascaded Use of Macros ...................... A "cascade" of macros is when one macro's body contains a reference to another macro. This is very common practice. For example, #define BUFSIZE 1020 #define TABLESIZE BUFSIZE This is not at all the same as defining `TABLESIZE' to be `1020'. The `#define' for `TABLESIZE' uses exactly the body you specify--in this case, `BUFSIZE'--and does not check to see whether it too is the name of a macro. It's only when you *use* `TABLESIZE' that the result of its expansion is checked for more macro names. This makes a difference if you change the definition of `BUFSIZE' at some point in the source file. `TABLESIZE', defined as shown, will always expand using the definition of `BUFSIZE' that is currently in effect: #define BUFSIZE 1020 #define TABLESIZE BUFSIZE #undef BUFSIZE #define BUFSIZE 37 Now `TABLESIZE' expands (in two stages) to `37'. File: cpp.info, Node: Conditionals, Next: Combining Sources, Prev: Macros, Up: Top Conditionals ============ In a macro processor, a "conditional" is a command that allows a part of the program to be ignored during compilation, on some conditions. In the C preprocessor, a conditional can test either an arithmetic expression or whether a name is defined as a macro. A conditional in the C preprocessor resembles in some ways an `if' statement in C, but it is important to understand the difference between them. The condition in an `if' statement is tested during the execution of your program. Its purpose is to allow your program to behave differently from run to run, depending on the data it is operating on. The condition in a preprocessor conditional command is tested when your program is compiled. Its purpose is to allow different code to be included in the program depending on the situation at the time of compilation. * Menu: * Uses: Conditional Uses. What conditionals are for. * Syntax: Conditional Syntax. How conditionals are written. * Deletion: Deleted Code. Making code into a comment. * Macros: Conditionals-Macros. Why conditionals are used with macros. * Errors: #error Command. Detecting inconsistent compilation parameters. File: cpp.info, Node: Conditional Uses, Next: Conditional Syntax, Prev: Conditionals, Up: Conditionals Why Conditionals are Used ------------------------- Generally there are three kinds of reason to use a conditional. * A program may need to use different code depending on the machine or operating system it is to run on. In some cases the code for one operating system may be erroneous on another operating system; for example, it might refer to library routines that do not exist on the other system. When this happens, it is not enough to avoid executing the invalid code: merely having it in the program makes it impossible to link the program and run it. With a preprocessor conditional, the offending code can be effectively excised from the program when it is not valid. * You may want to be able to compile the same source file into two different programs. Sometimes the difference between the programs is that one makes frequent time-consuming consistency checks on its intermediate data while the other does not. * A conditional whose condition is always false is a good way to exclude code from the program but keep it as a sort of comment for future reference. Most simple programs that are intended to run on only one machine will not need to use preprocessor conditionals. File: cpp.info, Node: Conditional Syntax, Next: Deleted Code, Prev: Conditional Uses, Up: Conditionals Syntax of Conditionals ---------------------- A conditional in the C preprocessor begins with a "conditional command": `#if', `#ifdef' or `#ifndef'. *Note Conditionals-Macros::, for info on `#ifdef' and `#ifndef'; only `#if' is explained here. * Menu: * If: #if Command. Basic conditionals using `#if' and `#endif'. * Else: #else Command. Including some text if the condition fails. * Elif: #elif Command. Testing several alternative possibilities. File: cpp.info, Node: #if Command, Next: #else Command, Prev: Conditional Syntax, Up: Conditional Syntax The `#if' Command ................. The `#if' command in its simplest form consists of #if EXPRESSION CONTROLLED TEXT #endif /* EXPRESSION */ The comment following the `#endif' is not required, but it is a good practice because it helps people match the `#endif' to the corresponding `#if'. Such comments should always be used, except in short conditionals that are not nested. In fact, you can put anything at all after the `#endif' and it will be ignored by the GNU C preprocessor, but only comments are acceptable in ANSI Standard C. EXPRESSION is a C expression of integer type, subject to stringent restrictions. It may contain * Integer constants, which are all regarded as `long' or `unsigned long'. * Character constants, which are interpreted according to the character set and conventions of the machine and operating system on which the preprocessor is running. The GNU C preprocessor uses the C data type `char' for these character constants; therefore, whether some character codes are negative is determined by the C compiler used to compile the preprocessor. If it treats `char' as signed, then character codes large enough to set the sign bit will be considered negative; otherwise, no character code is considered negative. * Arithmetic operators for addition, subtraction, multiplication, division, bitwise operations, shifts, comparisons, and `&&' and `||'. * Identifiers that are not macros, which are all treated as zero(!). * Macro calls. All macro calls in the expression are expanded before actual computation of the expression's value begins. Note that `sizeof' operators and `enum'-type values are not allowed. `enum'-type values, like all other identifiers that are not taken as macro calls and expanded, are treated as zero. The text inside of a conditional can include preprocessor commands. Then the commands inside the conditional are obeyed only if that branch of the conditional succeeds. The text can also contain other conditional groups. However, the `#if''s and `#endif''s must balance. File: cpp.info, Node: #else Command, Next: #elif Command, Prev: #if Command, Up: Conditional Syntax The `#else' Command ................... The `#else' command can be added to a conditional to provide alternative text to be used if the condition is false. This looks like #if EXPRESSION TEXT-IF-TRUE #else /* Not EXPRESSION */ TEXT-IF-FALSE #endif /* Not EXPRESSION */ If EXPRESSION is nonzero, and the TEXT-IF-TRUE is considered included, then `#else' acts like a failing conditional and the TEXT-IF-FALSE is ignored. Contrariwise, if the `#if' conditional fails, the TEXT-IF-FALSE is considered included. File: cpp.info, Node: #elif Command, Prev: #else Command, Up: Conditional Syntax The `#elif' Command ................... One common case of nested conditionals is used to check for more than two possible alternatives. For example, you might have #if X == 1 ... #else /* X != 1 */ #if X == 2 ... #else /* X != 2 */ ... #endif /* X != 2 */ #endif /* X != 1 */ Another conditional command, `#elif', allows this to be abbreviated as follows: #if X == 1 ... #elif X == 2 ... #else /* X != 2 and X != 1*/ ... #endif /* X != 2 and X != 1*/ `#elif' stands for ``else if''. Like `#else', it goes in the middle of a `#if'-`#endif' pair and subdivides it; it does not require a matching `#endif' of its own. Like `#if', the `#elif' command includes an expression to be tested. The text following the `#elif' is processed only if the original `#if'-condition failed and the `#elif' condition succeeeds. More than one `#elif' can go in the same `#if'-`#endif' group. Then the text after each `#elif' is processed only if the `#elif' condition succeeds after the original `#if' and any previous `#elif''s within it have failed. `#else' is equivalent to `#elif 1', and `#else' is allowed after any number of `#elif''s, but `#elif' may not follow a `#else'. File: cpp.info, Node: Deleted Code, Next: Conditionals-Macros, Prev: Conditional Syntax, Up: Conditionals Keeping Deleted Code for Future Reference ----------------------------------------- If you replace or delete a part of the program but want to keep the old code around as a comment for future reference, the easy way to do this is to put `#if 0' before it and `#endif' after it. This works even if the code being turned off contains conditionals, but they must be entire conditionals (balanced `#if' and `#endif'). File: cpp.info, Node: Conditionals-Macros, Next: #error Command, Prev: Deleted Code, Up: Conditionals Conditionals and Macros ----------------------- Conditionals are rarely useful except in connection with macros. A `#if' command whose expression uses no macros is equivalent to `#if 1' or `#if 0'; you might as well determine which one, by computing the value of the expression yourself, and then simplify the program. But when the expression uses macros, its value can vary from compilation to compilation. For example, here is a conditional that tests the expression `BUFSIZE == 1020', where `BUFSIZE' must be a macro. #if BUFSIZE == 1020 printf ("Large buffers!\n"); #endif /* BUFSIZE is large */ The special operator `defined' may be used in `#if' expressions to test whether a certain name is defined as a macro. Either `defined NAME' or `defined (NAME)' is an expression whose value is 1 if NAME is defined as macro at the current point in the program, and 0 otherwise. For the `defined' operator it makes no difference what the definition of the macro is; all that matters is whether there is a definition. Thus, for example, #if defined (vax) || defined (ns16000) would include the following code if either of the names `vax' and `ns16000' is defined as a macro. If a macro is defined and later undefined with `#undef', subsequent use of the `defined' operator will return 0, because the name is no longer defined. If the macro is defined again with another `#define', `defined' will recommence returning 1. Conditionals that test just the definedness of one name are very common, so there are two special short conditional commands for this case. They are `#ifdef NAME' is equivalent to `#if defined (NAME)'. `#ifndef NAME' is equivalent to `#if ! defined (NAME)'. Macro definitions can vary between compilations for several reasons. * Some macros are predefined on each kind of machine. For example, on a Vax, the name `vax' is a predefined macro. On other machines, it would not be defined. * Many more macros are defined by system header files. Different systems and machines define different macros, or give them different values. It is useful to test these macros with conditionals to avoid using a system feature on a machine where it is not implemented. * Macros are a common way of allowing users to customize a program for different machines or applications. For example, the macro `BUFSIZE' might be defined in a configuration file for your program that is included as a header file in each source file. You would use `BUFSIZE' in a preprocessor conditional in order to generate different code depending on the chosen configuration. * Macros can be defined or undefined with `-D' and `-U' command options when you compile the program. You can arrange to compile the same source file into two different programs by choosing a macro name to specify which program you want, writing conditionals to test whether or how this macro is defined, and then controlling the state of the macro with compiler command options. *Note Invocation::. File: cpp.info, Node: #error Command, Prev: Conditionals-Macros, Up: Conditionals The `#error' Command -------------------- The command `#error' causes the preprocessor to report a fatal error. The rest of the line that follows `#error' is used as the error message. You would use `#error' inside of a conditional that detects a combination of parameters which you know the program does not properly support. For example, if you know that the program will not run properly on a Vax, you might write #ifdef vax #error Won't work on Vaxen. See comments at get_last_object. #endif *Note Nonstandard Predefined::, for why this works. If you have several configuration parameters that must be set up by the installation in a consistent way, you can use conditionals to detect an inconsistency and report it with `#error'. For example, #if HASH_TABLE_SIZE % 2 == 0 || HASH_TABLE_SIZE % 3 == 0 \ || HASH_TABLE_SIZE % 5 == 0 #error HASH_TABLE_SIZE should not be divisible by a small prime #endif File: cpp.info, Node: Combining Sources, Next: Other Commands, Prev: Conditionals, Up: Top Combining Source Files ====================== One of the jobs of the C preprocessor is to inform the C compiler of where each line of C code came from: which source file and which line number. C code can come from multiple source files if you use `#include'; both `#include' and the use of conditionals and macros can cause the line number of a line in the preprocessor output to be different from the line's number in the original source file. You will appreciate the value of making both the C compiler (in error messages) and symbolic debuggers such as GDB use the line numbers in your source file. The C preprocessor builds on this feature by offering a command by which you can control the feature explicitly. This is useful when a file for input to the C preprocessor is the output from another program such as the `bison' parser generator, which operates on another file that is the true source file. Parts of the output from `bison' are generated from scratch, other parts come from a standard parser file. The rest are copied nearly verbatim from the source file, but their line numbers in the `bison' output are not the same as their original line numbers. Naturally you would like compiler error messages and symbolic debuggers to know the original source file and line number of each line in the `bison' output. `bison' arranges this by writing `#line' commands into the output file. `#line' is a command that specifies the original line number and source file name for subsequent input in the current preprocessor input file. `#line' has three variants: `#line LINENUM' Here LINENUM is a decimal integer constant. This specifies that the line number of the following line of input, in its original source file, was LINENUM. `#line LINENUM FILENAME' Here LINENUM is a decimal integer constant and FILENAME is a string constant. This specifies that the following line of input came originally from source file FILENAME and its line number there was LINENUM. Keep in mind that FILENAME is not just a file name; it is surrounded by doublequote characters so that it looks like a string constant. `#line ANYTHING ELSE' ANYTHING ELSE is checked for macro calls, which are expanded. The result should be a decimal integer constant followed optionally by a string constant, as described above. `#line' commands alter the results of the `__FILE__' and `__LINE__' predefined macros from that point on. *Note Standard Predefined::. File: cpp.info, Node: Other Commands, Next: Output, Prev: Combining Sources, Up: Top Miscellaneous Preprocessor Commands =================================== This section describes three additional preprocessor commands. They are not very useful, but are mentioned for completeness. The "null command" consists of a `#' followed by a Newline, with only whitespace (including comments) in between. A null command is understood as a preprocessor command but has no effect on the preprocessor output. The primary significance of the existence of the null command is that an input line consisting of just a `#' will produce no output, rather than a line of output containing just a `#'. Supposedly some old C programs contain such lines. The `#pragma' command is specified in the ANSI standard to have an arbitrary implementation-defined effect. In the GNU C preprocessor, `#pragma' commands are ignored, except for `#pragma once' (*note Once-Only::.). The `#ident' command is supported for compatibility with certain other systems. It is followed by a line of text. On certain systems, the text is copied into a special place in the object file; on most systems, the text is ignored and this directive has no effect. File: cpp.info, Node: Output, Next: Invocation, Prev: Other Commands, Up: Top C Preprocessor Output ===================== The output from the C preprocessor looks much like the input, except that all preprocessor command lines have been replaced with blank lines and all comments with spaces. Whitespace within a line is not altered; however, a space is inserted after the expansions of most macro calls. Source file name and line number information is conveyed by lines of the form # LINENUM FILENAME FLAG which are inserted as needed into the middle of the input (but never within a string or character constant). Such a line means that the following line originated in file FILENAME at line LINENUM. The third field, FLAG, may be a number, or may be absent. It is `1' for the beginning of a new source file, and `2' for return to an old source file at the end of an included file. It is absent otherwise. File: cpp.info, Node: Invocation, Next: Concept Index, Prev: Output, Up: Top Invoking the C Preprocessor =========================== Most often when you use the C preprocessor you will not have to invoke it explicitly: the C compiler will do so automatically. However, the preprocessor is sometimes useful individually. The C preprocessor expects two file names as arguments, INFILE and OUTFILE. The preprocessor reads INFILE together with any other files it specifies with `#include'. All the output generated by the combined input files is written in OUTFILE. Either INFILE or OUTFILE may be `-', which as INFILE means to read from standard input and as OUTFILE means to write to standard output. Also, if OUTFILE or both file names are omitted, the standard output and standard input are used for the omitted file names. Here is a table of command options accepted by the C preprocessor. Most of them can also be given when compiling a C program; they are passed along automatically to the preprocessor when it is invoked by the compiler. `-P' Inhibit generation of `#'-lines with line-number information in the output from the preprocessor (*note Output::.). This might be useful when running the preprocessor on something that is not C code and will be sent to a program which might be confused by the `#'-lines `-C' Do not discard comments: pass them through to the output file. Comments appearing in arguments of a macro call will be copied to the output before the expansion of the macro call. `-trigraphs' Process ANSI standard trigraph sequences. These are three-character sequences, all starting with `??', that are defined by ANSI C to stand for single characters. For example, `??/' stands for `\', so `'??/n'' is a character constant for a newline. Strictly speaking, the GNU C preprocessor does not support all programs in ANSI Standard C unless `-trigraphs' is used, but if you ever notice the difference it will be with relief. You don't want to know any more about trigraphs. `-pedantic' Issue warnings required by the ANSI C standard in certain cases such as when text other than a comment follows `#else' or `#endif'. `-I DIRECTORY' Add the directory DIRECTORY to the end of the list of directories to be searched for header files (*note Include Syntax::.). This can be used to override a system header file, substituting your own version, since these directories are searched before the system header file directories. If you use more than one `-I' option, the directories are scanned in left-to-right order; the standard system directories come after. `-I-' Any directories specified with `-I' options before the `-I-' option are searched only for the case of `#include "FILE"'; they are not searched for `#include <FILE>'. If additional directories are specified with `-I' options after the `-I-', these directories are searched for all `#include' directives. In addition, the `-I-' option inhibits the use of the current directory as the first search directory for `#include "FILE"'. Therefore, the current directory is searched only if it is requested explicitly with `-I.'. Specifying both `-I-' and `-I.' allows you to control precisely which directories are searched before the current one and which are searched after. `-nostdinc' Do not search the standard system directories for header files. Only the directories you have specified with `-I' options (and the current directory, if appropriate) are searched. `-D NAME' Predefine NAME as a macro, with definition `1'. `-D NAME=DEFINITION' Predefine NAME as a macro, with definition DEFINITION. There are no restrictions on the contents of DEFINITION, but if you are invoking the preprocessor from a shell or shell-like program you may need to use the shell's quoting syntax to protect characters such as spaces that have a meaning in the shell syntax. `-U NAME' Do not predefine NAME. If both `-U' and `-D' are specified for one name, the `-U' beats the `-D' and the name is not predefined. `-undef' Do not predefine any nonstandard macros. `-d' Instead of outputting the result of preprocessing, output a list of `#define' commands for all the macros defined during the execution of the preprocessor. `-M' Instead of outputting the result of preprocessing, output a rule suitable for `make' describing the dependencies of the main source file. The preprocessor outputs one `make' rule containing the object file name for that source file, a colon, and the names of all the included files. If there are many included files then the rule is split into several lines using `\'-newline. This feature is used in automatic updating of makefiles. `-MM' Like `-M' but mention only the files included with `#include "FILE"'. System header files included with `#include <FILE>' are omitted. `-i FILE' Process FILE as input, discarding the resulting output, before processing the regular input file. Because the output generated from FILE is discarded, the only effect of `-i FILE' is to make the macros defined in FILE available for use in the main input. File: cpp.info, Node: Concept Index, Next: Index, Prev: Invocation, Up: Top Concept Index ************* * Menu: * cascaded macros: Cascaded Macros. * commands: Commands. * concatenation: Concatenation. * conditionals: Conditionals. * header file: Header Files. * line control: Combining Sources. * macro body uses macro: Cascaded Macros. * null command: Other Commands. * options: Invocation. * output format: Output. * predefined macros: Predefined. * preprocessor commands: Commands. * redefining macros: Redefining. * repeated inclusion: Once-Only. * self-reference: Self-Reference. * semicolons (after macro calls): Swallow Semicolon. * side effects (in macro arguments): Side Effects. * stringification: Stringification. * undefining macros: Undefining. * unsafe macros: Side Effects. File: cpp.info, Node: Index, Prev: Concept Index, Up: Top Index of Commands, Macros and Options ************************************* * Menu: * #elif: #elif Command. * #else: #else Command. * #error: #error Command. * #ident: Other Commands. * #if: Conditional Syntax. * #ifdef: Conditionals-Macros. * #ifndef: Conditionals-Macros. * #include: Include Syntax. * #line: Combining Sources. * #pragma: Other Commands. * -C: Invocation. * -D: Invocation. * -I: Invocation. * -M: Invocation. * -MM: Invocation. * -P: Invocation. * -U: Invocation. * -d: Invocation. * -i: Invocation. * -pedantic: Invocation. * -trigraphs: Invocation. * -undef: Invocation. * BSD: Nonstandard Predefined. * M68020: Nonstandard Predefined. * __BASE_FILE__: Standard Predefined. * __DATE__: Standard Predefined. * __FILE__: Standard Predefined. * __LINE__: Standard Predefined. * __STDC__: Standard Predefined. * __TIME__: Standard Predefined. * defined: Conditionals-Macros. * m68k: Nonstandard Predefined. * mc68000: Nonstandard Predefined. * ns32000: Nonstandard Predefined. * pyr: Nonstandard Predefined. * sequent: Nonstandard Predefined. * sun: Nonstandard Predefined. * system header files: Header Uses. * unix: Nonstandard Predefined. * vax: Nonstandard Predefined. Tag Table: Node: Top750 Node: Global Actions3306 Node: Commands5811 Node: Header Files7416 Node: Header Uses7992 Node: Include Syntax9379 Node: Include Operation12392 Node: Once-Only14058 Node: Macros15869 Node: Simple Macros16781 Node: Argument Macros19828 Node: Predefined24918 Node: Standard Predefined25346 Node: Nonstandard Predefined29551 Node: Stringification32833 Node: Concatenation35672 Node: Undefining38930 Node: Redefining39952 Node: Macro Pitfalls41238 Node: Misnesting42281 Node: Macro Parentheses43289 Node: Swallow Semicolon45144 Node: Side Effects47032 Node: Self-Reference48718 Node: Argument Prescan50967 Node: Cascaded Macros55931 Node: Conditionals56952 Node: Conditional Uses58240 Node: Conditional Syntax59627 Node: #if Command60196 Node: #else Command62447 Node: #elif Command63094 Node: Deleted Code64437 Node: Conditionals-Macros64968 Node: #error Command68190 Node: Combining Sources69234 Node: Other Commands71848 Node: Output73081 Node: Invocation74012 Node: Concept Index79436 Node: Index80238