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A variadic macro is a feature of some computer programming languages, especially the C preprocessor, whereby a macro may be declared to accept a varying number of arguments. Variable-argument macros were introduced in 1999 in the ISO/IEC 9899:1999 ( C99 ) revision of the C language standard, and in 2011 in ISO/IEC 14882:2011 ( C++11 ) revision ...
One little-known usage pattern of the C preprocessor is known as X-Macros. [6] [7] [8] An X-Macro is a header file. Commonly, these use the extension .def instead of the traditional .h. This file contains a list of similar macro calls, which can be referred to as "component macros." The include file is then referenced repeatedly.
A parameterized macro is a macro that is able to insert given objects into its expansion. This gives the macro some of the power of a function. As a simple example, in the C programming language, this is a typical macro that is not a parameterized macro, i.e., a parameterless macro: #define PI 3.14159
Unlike some other macro processors, m4 is Turing-complete as well as a practical programming language. Unquoted identifiers which match defined macros are replaced with their definitions. Placing identifiers in quotes suppresses expansion until possibly later, such as when a quoted string is expanded as part of macro replacement.
Examples of such lists particularly include initialization of arrays, in concert with declarations of enumeration constants and function prototypes; generation of statement sequences and switch arms; etc. Usage of X macros dates back to the 1960s. [1] It remains useful in modern-day C and C++ programming languages, but remains relatively ...
UTF-8 and Shift JIS are often used in C byte strings, while UTF-16 is often used in C wide strings when wchar_t is 16 bits. Truncating strings with variable-width characters using functions like strncpy can produce invalid sequences at the end of the string. This can be unsafe if the truncated parts are interpreted by code that assumes the ...
C's offsetof() macro is an ANSI C library feature found in stddef.h. It evaluates to the offset (in bytes) of a given member within a struct or union type, an expression of type size_t . The offsetof() macro takes two parameters , the first being a structure or union name, and the second being the name of a subobject of the structure/union that ...
In C23 the second argument is optional and will not be evaluated. [2] After this, each invocation of the va_arg macro yields the next argument. The first argument to va_arg is the va_list and the second is the type of the next argument passed to the function. As the last step, the va_end macro must be called on the va_list before the function ...