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#include <stdarg.h>va_list pvar;
void va_start(va_list pvar, parmN);
type va_arg(va_list pvar, type);
void va_end(va_list pvar);
va_list is a type defined for the variable used to traverse the list.
The va_start macro is invoked before any access to the unnamed arguments and initializes pvar for subsequent use by va_arg and va_end. The parameter parmN is the identifier of the rightmost parameter in the variable parameter list in the function definition (the one just before the , ...). If this parameter is declared with the register storage class or with a function or array type, or with a type that is not compatible with the type that results after application of the default argument promotions, the behavior is undefined.
The parameter parmN is required under strict ANSI C compilation. In other compilation modes, parmN need not be supplied and the second parameter to the va_start macro can be left empty [e.g., va_start(pvar, );]. This allows for routines that contain no parameters before the ... in the variable parameter list.
The va_arg macro expands to an expression that has the type and value of the next argument in the call. The parameter pvar should have been previously initialized by va_start. Each invocation of va_arg modifies pvar so that the values of successive arguments are returned in turn. The parameter type is the type name of the next argument to be returned. The type name must be specified in such a way so that the type of a pointer to an object that has the specified type can be obtained simply by postfixing a * to type. If there is no actual next argument, or if type is not compatible with the type of the actual next argument (as promoted according to the default argument promotions), the behavior is undefined.
The va_end macro is used to clean up.
Multiple traversals, each bracketed by va_start and va_end, are possible.
#include <stdarg.h> #define MAXARGS 31void f1(int n_ptrs, ...) { va_list ap; char array[MAXARGS]; int ptr_no = 0;
if (n_ptrs > MAXARGS) n_ptrs = MAXARGS; va_start(ap, n_ptrs); while (ptr_no < n_ptrs) array[ptr_no++] = va_arg(ap, char); va_end(ap); f2(n_ptrs, array); }
Each call to f1 shall have visible the definition of the function or a declaration such as
void f1(int, ...)