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stdarg.h File Reference

Standard C Libraries -. More...

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Macros

#define va_arg(ap, Ty)
 
#define va_end(ap)   (void)0
 
#define va_start(ap, last_arg)   AP=(void *) __builtin_next_arg (LASTARG)
 

Detailed Description

Standard C Libraries -.

Compiler:
MPLAB XC16 compiler

Description

The header file, stdarg.h, supports functions with variable argument lists. This allows functions to have arguments without corresponding parameter declarations. There must be at least one named argument. The variable arguments are represented by ellipses (...). An object of type, va_list, must be declared inside the function to hold the arguments. va_start will initialize the variable to an argument list, va_arg will access the argument list, and va_end will end the use of the argument.

Software License Agreement

The documentation in this header file has been copied from the documentation provided with the Microchip MPLAB XC16 compiler. The original license agreement included with the XC16 compiler applies!

Macro Definition Documentation

#define va_arg (   ap,
  Ty 
)
Value:
(AP = (void *) ((char *) (AP) - __va_rounded_size (TYPE)), \
*((TYPE *) (void *) ((char *) (AP) )))

Description: The type va_list declares a variable that will refer to each argument in a variable-length argument list.

Include: <stdarg.h>

Example:
See va_arg. Description: Gets the current argument.

Include: <stdarg.h>

Parameters
appointer to list of arguments
Tytype of argument to be retrieved
Returns
Returns the current argument

Remarks:
va_start must be called before va_arg.

Example:

#include <stdio.h> // for printf
#include <stdarg.h> // for va_arg, va_start,
va_list, va_end
void tprint(const char *fmt, ...) {
va_list ap;
va_start(ap, fmt);
while (*fmt) {
switch (*fmt) {
case '%':
fmt++;
if (*fmt == 'd') {
int d = va_arg(ap, int);
printf("<%d> is an integer\n", d);
} else if (*fmt == 's') {
char *s = va_arg(ap, char*);
printf("<%s> is a string\n", s);
} else {
printf("%%%c is an unknown format\n",
fmt);
}
fmt++;
break;
default:
printf("%c is unknown\n", *fmt);
fmt++;
break;
}
}
va_end(ap);
}
int main(void) {
tprint("%d%s.%c", 83, "This is text.", 'a');
}

Output:
<83> is an integer
<This is text.> is a string
. is unknown
%c is an unknown format

#define va_end (   ap)    (void)0

Description: Ends the use of ap.

Include: <stdarg.h>

Parameters
appointer to list of arguments

Remarks:
After a call to va_end, the argument list pointer, ap, is considered to be invalid. Further calls to va_arg should not be made until the next va_start. In the 16-bit compiler, va_end does nothing, so this call is not necessary but should be used for readability and portability.

Example:
See va_arg.

#define va_start (   ap,
  last_arg 
)    AP=(void *) __builtin_next_arg (LASTARG)

Description: Sets the argument pointer ap to first optional argument in the variable-length argument list.

Include: <stdarg.h>

Parameters
appointer to list of arguments
last_arglast named argument before the optional arguments

Example:
See va_arg.