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A compiler with support for the OpenMP parallelization library can automatically parallelize a for loop with #pragma omp parallel for. It is called a macro processor because it allows you to define macros, which are brief abbreviations for longer constructs. This is called token pasting or token concatenation. The C standard says that this condition provokes undefined behavior, so GCC will emit a warning message.

Once-Only Headers If a header file happens to be included twice, the compiler will process its contents twice. Also, you cannot rely on it preserving characteristics of the input which are not significant to C-family languages. You can even split /*, */, and // onto multiple lines with backslash-newline. Including a header file produces the same results as copying the header file into each source file that needs it.

Parameters are not replaced inside string constants, but you can use the # preprocessing operator instead. Here is an example: #define lprintf(...) fprintf (log, __VA_ARGS__) This kind of macro is called variadic. A program example: #include #include #include #include void TestString(char *string); void main() { // first test array of char, 10 characters... // should It is defined to 1.

The C compiler will almost certainly reject source code containing "other" tokens. In C++, there is a fourth category, the named operators. gnu.org. ^ "Using the fpp Preprocessor". You could do this with a series of conditionals, #if SYSTEM_1 # include "system_1.h" #elif SYSTEM_2 # include "system_2.h" #elif SYSTEM_3 ... #endif That rapidly becomes tedious.

You should not refer to this macro yourself; instead, refer to the standard macros defined in limits.h. __CHAR_BIT__ Defined to the number of bits used in the representation of the

Support for the 1999 revision is not yet complete. But s is an ordinary argument to xstr, so it is completely macro-expanded before xstr itself is expanded (see Argument Prescan). Retrieved 27 October 2008. ^ a b "The C Preprocessor: Overview". A #line directive changes __LINE__, and may change __FILE__ as well.

The line numbers do not appear in the source file. 10.9 Predefined Macros There are standard predefined macros as shown in Table 10.1. Internal whitespace sequences are each replaced with a single space. For example, #define BUFFER_SIZE 1024 defines a macro named BUFFER_SIZE as an abbreviation for the token 1024. Both the tokens combined by ## could come from the macro body, but you could just as well write them as one token in the first place.

Preprocessor Overview Header Files Macros Conditionals Pragmas Other Directives User-defined Diagnostics Line Control Preprocessor Output C Preprocessor Command-Line Options Traditional Mode Implementation Details History GNU General Public License GNU Free Documentation You can however write a series of adjacent string constants and stringified arguments: the C compiler will then combine all the adjacent string constants into one long string. Retrieved 17 July 2016. ^ "1.3 Preprocessing and conditional compilation". Macro Arguments Variadic Macros Macro Arguments Function-like macros can take arguments, just like true functions.

cout<<"Insert two integers: "; cin>>x>>y; cout<<"Do the assert(x < y)\n"; // if x < y, it is OK, else this program will terminate... A hosted environment has the complete facilities of the standard C library available. Keyword pragma is part of the C++ standard, but the form, content, and meaning of pragma is different for every compiler. There is no limit on the length of a character constant, but the value of a character constant that contains more than one character is implementation-defined.

There are, however, two ways to make normal headers into system headers. Note that the WHERESTR argument is concatenated with the string following it. This manual discusses the GNU C preprocessor, which provides a small superset of the features of ISO Standard C. So CPP retains the comma when conforming to a specific C standard, and drops it otherwise.

For example the following statement contains 6 tokens. Some macros are automatically defined for you. Exponents are the two-character sequences e+, e-, E+, E-, p+, p-, P+, and P-. (The exponents that begin with p or P are new to C99. Their exact behavior may depend on command-line flags supplied on invocation.

For example: #if (MyVAL != 2 && MyVAL != 3) #error MyVAL must be defined to either 2 or 3 #endif Then, when you compile the following simple program: // the The gcc documentation recommends to quote the message. Line comments are not in the 1989 edition of the C standard, but they are recognized by GCC as an extension. For example, #define NUMBERS 1, \ 2, \ 3 int x[] = { NUMBERS }; expands to int x[] = { 1, 2, 3 }; The most common visible consequence of

C "Preprocessor Trick For Implementing Similar Data Types". Thus, #include specifies inclusion of a system header file named x/*y. This is unlikely to cause problems if you use double-quote includes, which are close enough to string constants. Macro expansion.

Traditional C compilers do not recognize this idiom. But it appears parse correctly (as all #pragmas should be) so it is portable in that sense. –nolandda Jun 14 '13 at 20:16 2 In MSVC 2008 #pragma message does For example, min(min(a,b),c) is first expanded to min (((a) < (b) ? (a) : (b)), (c)) and then to ((((a) < (b) ? (a) : (b))) < (c) ? (((a) <