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> |
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|---|---|
| enables access to variadic function arguments (function macro) |
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| accesses the next variadic function argument (function macro) |
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(C++11) | makes a copy of the variadic function arguments (function macro) |
| ends traversal of the variadic function arguments (function macro) |
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| holds the information needed by va_start, va_arg, va_end, and va_copy (typedef) |
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#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
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