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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 ...
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.
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 This causes PI to always be replaced with 3.14159 wherever it occurs. An example of a parameterized macro, on the other hand, is this: #define pred(x) ((x)-1)
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 defines macros for printf format string and scanf format string specifiers corresponding to the types defined in <stdint.h> and several functions for working with the intmax_t and uintmax_t types. This header was added in C99 .
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 ...
For example, given int i = 1; j = 2;, the result of max(i,j) is 2. If a and b were only evaluated once, the result of max(i++,j++) would be the same, but with double evaluation the result is 3. Hidden order of operation. Failure to bracket arguments can lead to unexpected results. For example, a macro to double a value might be written as:
Macros are then implemented by allowing registers and stack entries to be strings as well as numbers. A string can be printed, but it can also be executed (i.e. processed as a sequence of dc commands). So for instance we can store a macro to add one and then multiply by 2 into register m: [1 + 2 *] sm