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Variadic functions

From cppreference.com
< c

Variadic functions are functions (e.g. printf) which take a variable number of arguments.

The declaration of a variadic function uses an ellipsis as the last parameter, e.g. int printf(const char* format, ...);. See variadic arguments for additional detail on the syntax and automatic argument conversions.

Accessing the variadic arguments from the function body uses the following library facilities:

Contents

Types
holds the information needed by va_start, va_arg, va_end, and va_copy
(typedef) [edit]
Macros
Defined in header <stdarg.h>
enables access to variadic function arguments
(function macro) [edit]
accesses the next variadic function argument
(function macro) [edit]
makes a copy of the variadic function arguments
(function macro) [edit]
ends traversal of the variadic function arguments
(function macro) [edit]

[edit] Example

Print values of different types.

#include <stdarg.h> #include <stdio.h>   void simple_printf(const char* fmt, ...) { va_list args;   for (va_start(args, fmt); *fmt != '\0'; ++fmt) { switch(*fmt) { case 'd': { int i = va_arg(args, int); printf("%d\n", i); break; } case 'c': { // A 'char' variable will be promoted to 'int' // A character literal in C is already 'int' by itself int c = va_arg(args, int); printf("%c\n", c); break; } case 'f': { double d = va_arg(args, double); printf("%f\n", d); break; } default: puts("Unknown formatter!"); goto END; } } END: va_end(args); }   int main(void) { simple_printf("dcff", 3, 'a', 1.969, 42.5); }

Output:

3 a 1.969000 42.50000

[edit] References

  • C23 standard (ISO/IEC 9899:2024):
  • 7.16 Variable arguments <stdarg.h> (p: TBD)
  • C17 standard (ISO/IEC 9899:2018):
  • 7.16 Variable arguments <stdarg.h> (p: TBD)
  • C11 standard (ISO/IEC 9899:2011):
  • 7.16 Variable arguments <stdarg.h> (p: 269-272)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.15 Variable arguments <stdarg.h> (p: 249-252)
  • C89/C90 standard (ISO/IEC 9899:1990):
  • 4.8 VARIABLE ARGUMENTS <stdarg.h>

[edit] See also

C++ documentation for Variadic functions