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#include <pfmt.h> #include <stdarg.h> int vlfmt(FILE *stream, long flag, const char *format, va_list ap);
The vlfmt() function is identical to lfmt(3C), except that it is called with an argument list as defined by <stdarg.h>.
The <stdarg.h> header defines the type va_list and a set of macros for advancing through a list of arguments whose number and types may vary. The ap argument is of type va_list. This argument is used with the <stdarg.h> macros va_start(), va_arg(), and va_end(). See stdarg(3EXT). The example in the EXAMPLES section below demonstrates their use with vlfmt().
Upon successful completion, vlfmt() returns the number of bytes transmitted. Otherwise, -1 is returned if there was a write error to stream, or -2 is returned if unable to log and/or display at console.
Example 1 Use of vlfmt() to write an errlog()routine.
The following example demonstrates how vlfmt() could be used to write an errlog() routine. The va_alist() macro is used as the parameter list in a function definition. The va_start(ap, .\|.\|.) call, where ap is of type va_list, must be invoked before any attempt to traverse and access unnamed arguments. Calls to va_arg(ap, atype) traverse the argument list. Each execution of va_arg() expands to an expression with the value and type of the next argument in the list ap, which is the same object initialized by va_start(). The atype argument is the type that the returned argument is expected to be. The va_end(ap) macro must be invoked when all desired arguments have been accessed. The argument list in ap can be traversed again if va_start() is called again after va_end().) In the example below, va_arg() is executed first to retrieve the format string passed to errlog(). The remaining errlog() arguments (arg1, arg2, ...) are passed to vlfmt() in the argument ap.
#include <pfmt.h>
#include <stdarg.h>
/*
* errlog should be called like
* errlog(log_info, format, arg1, ...);
*/
void errlog(long log_info, ...)
{
va_list ap;
char *format;
va_start(ap, );
format = va_arg(ap, char *);
(void) vlfmt(stderr, log_info|MM_ERROR, format, ap);
va_end(ap);
(void) abort();
}
Since vlfmt() uses gettxt(3C), it is recommended that vlfmt() not be used.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE ATTRIBUTE VALUE |
| MT-Level MT-Safe |
gettxt(3C), lfmt(3C), attributes(5), stdarg(3EXT)