# Variadic functions

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< cpp‎ | utility

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>`
va_start | enables access to variadic function arguments (function macro)
va_arg | accesses the next variadic function argument (function macro)
va_copy (C++11) | makes a copy of the variadic function arguments (function macro)
va_end | ends traversal of the variadic function arguments (function macro)
va_list | 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

### See also

C documentation for Variadic functions

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