Difference between revisions of "c/variadic"
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Revision as of 03:53, 8 June 2015
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:
Macros | ||
| Defined in header
<stdarg.h> | ||
| enables access to variadic function arguments (function macro) | ||
| accesses the next variadic function argument (function macro) | ||
| (C99) |
makes a copy of the variadic function arguments (function macro) | |
| ends traversal of the variadic function arguments (function macro) | ||
Type | ||
| holds the information needed by va_start, va_arg, va_end, and va_copy (typedef) | ||
Example
Print values of different types.
Run this code
#include <stdio.h> #include <stdarg.h> void simple_printf(const char* fmt,...) { va_list args; va_start(args, fmt); while (*fmt != '\0') { if (*fmt == 'd') { int i = va_arg(args, int); printf("%d\n", i); } else if (*fmt == 'c') { // note automatic conversion to integral type int c = va_arg(args, int); printf("%c\n", c); } else if (*fmt == 'f') { double d = va_arg(args, double); printf("%f\n", d); } ++fmt; } va_end(args); } int main(void) { simple_printf("dcff", 3, 'a', 1.999, 42.5); }
Output:
3 a 1.999000 42.50000
References
- 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>
See also
| C++ documentation for Variadic functions
|
