C++ <cstdarg> - va_start
The C++ <cstdarg> va_start macro enables access to the additional arguments following the named argument parm_n.
va_start should be invoked first with the list of variable arguments as a va_list before any calls to va_arg. After the call, it carries the information needed to retrieve the additional arguments using va_arg. A function that invokes va_start, shall also invoke va_end before it returns.
Syntax
void va_start( va_list ap, parm_n );
Parameters
ap |
Specify an instance of the va_list type. |
parm_n |
Specify the named parameter preceding the first variable parameter. The arguments extracted by subsequent calls to va_arg are those after parm_n.
If this parameter is declared with reference type or with a type not compatible with the type that results from default argument promotions, the behavior is undefined. |
Return Value
None.
Example:
The example below shows the usage of va_start macro function.
#include <iostream> #include <cstdarg> using namespace std; int add_nums(int count, ...) { int result = 0; va_list args; va_start(args, count); for (int i = 0; i < count; ++i) { result += va_arg(args, int); } va_end(args); return result; } int main () { cout<<"Sum is: "<<add_nums (2, 10, 20)<<"\n"; cout<<"Sum is: "<<add_nums (3, 10, 20, 30)<<"\n"; cout<<"Sum is: "<<add_nums (4, 10, 20, 30, 40)<<"\n"; return 0; }
The output of the above code will be:
Sum is: 30 Sum is: 60 Sum is: 100
❮ C++ <cstdarg> Library