17 Language support library [support]

17.13 Other runtime support [support.runtime]

17.13.2 Header <cstdarg> synopsis [cstdarg.syn]

// all freestanding namespace std { using va_list = see below; } #define va_arg(V, P) see below #define va_copy(VDST, VSRC) see below #define va_end(V) see below #define va_start(V, P) see below
The contents of the header <cstdarg> are the same as the C standard library header <stdarg.h>, with the following changes:
  • In lieu of the default argument promotions specified in ISO/IEC 9899:2018, the definition in [expr.call] applies.
  • The restrictions that C places on the second parameter to the va_start macro in header <stdarg.h> are different in this document.
    The parameter parmN is the rightmost parameter in the variable parameter list of the function definition (the one just before the ...).195
    If the parameter parmN is a pack expansion ([temp.variadic]) or an entity resulting from a lambda capture ([expr.prim.lambda]), the program is ill-formed, no diagnostic required.
    If the parameter parmN is of a reference type, or of a type that is not compatible with the type that results when passing an argument for which there is no parameter, the behavior is undefined.
See also: ISO/IEC 9899:2018,
Note that va_start is required to work as specified even if unary operator& is overloaded for the type of parmN.