stdarg(3STDC)

NAME | SYNOPSIS | API RESTRICTIONS | DESCRIPTION | EXAMPLES | STANDARDS | COMPATIBILITY | RESTRICTIONS | ATTRIBUTES

NAME

stdarg- variable argument lists

SYNOPSIS

#include <stdarg.h>

void va_start(va_list ap, last);
type va_arg(va_list ap, type);
void va_end(va_list ap);

API RESTRICTIONS

The function or functions documented here may not be used safely in all application contexts with all APIs provided in the ChorusOS 5.0 product.

See API(5FEA) for details.

DESCRIPTION

A function may be called with a varying number of arguments of several different types. The include file declares a type va_list and defines three macros for stepping through a list of arguments whose number and types are not known to the function called.

The function called must declare an object of type va_list which is used by the macros va_start(), va_arg() and va_end().

The va_start() macro initializes ap for subsequent use by va_arg() and va_end(), and must be called first.

The parameter last is the name of the last parameter before the variable argument list. In other words, the last parameter of which the calling function knows the type.

Because the address of this parameter is used in the va_start() macro, it should not be declared as a register variable, or as a function or an array type.

The va_start() macro does not return a value.

The va_arg() macro expands to an expression that has the type and value of the next argument in the call. The parameter ap is the va_list initialized by va_start(). Each call to va_arg() modifies ap so that the next call returns the next argument. 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 next argument, or if type is not compatible with the actual type of the next argument (as promoted according to the default argument promotions), random errors will occur.

The first use of the va_arg() macro after that of the va_start() macro returns the argument after last. Successive invocations return the values of the remaining arguments.

The va_end() macro handles a normal return from the function whose variable argument list was initialized using va_start().

The va_end() macro does not return a value.

EXAMPLES

---

void foo(char *fmt, ...)
{
        va_list ap;
        int d;
        char c, *p, *s;
        va_start(ap, fmt);
        while (*fmt)
                switch(*fmt++) {
                case 's':                       /* string */
                        s = va_arg(ap, char *);
                        printf("string %s\n", s);
                        break;
                case 'd':                       /* int */
                        d = va_arg(ap, int);
                        printf("int %d\n", d);
                        break;
                case 'c':                       /* char */
                        c = va_arg(ap, char);
                        printf("char %c\n", c);
                        break;
                }
        va_end(ap);
}

---

STANDARDS

The va_start(), va_arg() and va_end() macros conform to ANSI-C.

COMPATIBILITY

These macros are not compatible with the macros they replace. A backward-compatible version can be found in the include file varargs.h.

RESTRICTIONS

Unlike the varargs() macros, the stdarg() macros do not permit programmers to code a function with no fixed arguments.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Evolving

NAME | SYNOPSIS | API RESTRICTIONS | DESCRIPTION | EXAMPLES | STANDARDS | COMPATIBILITY | RESTRICTIONS | ATTRIBUTES