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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 ...
A macro specifies how to replace text in the source code with other text. An object-like macro defines a token that the preprocessor replaces with other text. It does not include parameter syntax and therefore cannot support parameterization. The following macro definition associates the text "1 / 12" with the token "VALUE":
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
This example aims to improve the readability of the X macro usage by: Prefix the name of the macro that defines the list with "FOR_". Pass name of the worker macro into the list macro. This both avoids defining an obscurely named macro (X), and alleviates the need to undefine it. Use the syntax for variadic macro arguments "..." in the worker ...
According to the standard, to access the unnamed arguments it can be through a variable of type va_list in the variadic function, with macro va_start also provided as the last named parameter of the function. 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 ...
Any new expression that uses the placement syntax is a placement new expression, and any operator new or operator delete function that takes more than the mandatory first parameter (std:: size_t) is a placement new or placement delete function. [4] A placement new function takes two input parameters: std:: size_t and void *.
The basic variadic facility in C++ is largely identical to that in C. The only difference is in the syntax, where the comma before the ellipsis can be omitted. C++ allows variadic functions without named parameters but provides no way to access those arguments since va_start requires the name of the last fixed argument of the function.
The assert macro implements runtime assertion. If the expression within it is false, the macro will print a message to stderr and call abort(), defined in stdlib.h.The message includes the source filename and the source line number from the macros __FILE__ and __LINE__, respectively. [2]