Variadic functions
Variadic functions are functions (e.g. std::printf) which take a variable number of arguments.
To declare a variadic function, an ellipsis is used as the last parameter, e.g. int printf(const char* format, ...);. See Variadic arguments for additional detail on the syntax, automatic argument conversions and the alternatives.
To access the variadic arguments from the function body, the following library facilities are provided:
Defined in header
<cstdarg> | |
enables access to variadic function arguments (function macro) | |
accesses the next variadic function argument (function macro) | |
(C++11) |
makes a copy of the variadic function arguments (function macro) |
ends traversal of the variadic function arguments (function macro) | |
holds the information needed by va_start, va_arg, va_end, and va_copy (typedef) |
Example
Run this code
#include <iostream> #include <cstdarg> 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); std::cout << i << '\n'; } else if (*fmt == 'c') { // note automatic conversion to integral type int c = va_arg(args, int); std::cout << static_cast<char>(c) << '\n'; } else if (*fmt == 'f') { double d = va_arg(args, double); std::cout << d << '\n'; } ++fmt; } va_end(args); } int main() { simple_printf("dcff", 3, 'a', 1.999, 42.5); }
Output:
3 a 1.999 42.5