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#include <pfmt.h> #include <stdarg.h> int vpfmt(FILE *stream, long flag, const char *format, va_list ap);
The vpfmt() function is identical to pfmt(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 vpfmt().
Upon successful completion, vpfmt() returns the number of bytes transmitted. Otherwise, -1 is returned if there was a write error to stream.
Example 1 Use of vpfmt() to write an error routine.
The following example demonstrates how vpfmt() could be used to write an error() 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 error(). The remaining error() arguments (arg1, arg2, ...) are passed to vpfmt() in the argument ap.
#include <pfmt.h> #include <stdarg.h> /* * error should be called like * error(format, arg1, ...); */ void error(...) { va_list ap; char *format; va_start(ap, ); format = va_arg(ap, char *); (void) vpfmt(stderr, MM_ERROR, format, ap); va_end(ap); (void) abort(); }
Since vpfmt() uses gettxt(3C), it is recommended that vpfmt() not be used.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE ATTRIBUTE VALUE |
| MT-Level MT-Safe |
gettxt(3C), pfmt(3C), attributes(5), stdarg(3EXT)