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The __VA_OPT__ macro is replaced by its argument when arguments are present, and omitted otherwise. Common compilers also permit passing zero arguments before this addition, however. [4] [6] The C preprocessor rules prevent macro names in the argument of __VA_OPT__ from expanding recursively. It is possible to work around this limitation up to ...
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 ...
It has explicit input and output operators, unlike the typical implicit I/O at the outermost macro level, which makes it simultaneously simpler and more versatile [vague] than older macro languages. TRAC is a text-processing language, [5] also called a string processing language. [6] Because of this the only data type available is a string of ...
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
One little-known usage pattern of the C preprocessor is known as X-Macros. [5] [6] [7] 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.
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 ...
If the macro __STDC_UTF_16__ is defined as 1, the type is used for UTF-16 on that system. This is always the case in C23. [15] C++ does not define such a macro, but the type is always used for UTF-16 in that language. [16] char32_t [13] Part of the C standard since C11, [17] in <uchar.h>, a type capable of holding 32 bits even if wchar_t is ...
In the C programming language, Duff's device is a way of manually implementing loop unrolling by interleaving two syntactic constructs of C: the do-while loop and a switch statement. Its discovery is credited to Tom Duff in November 1983, when Duff was working for Lucasfilm and used it to speed up a real-time animation program.