# 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 appears after the list of parameters, e.g. int printf(const char* format...);, which may be preceded by an optional comma. 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 <cstdarg>
    #include <iostream>

    void simple_printf(const char* fmt...) // C-style "const char* fmt, ..." is also valid
    {
        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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