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BSD 2.11 - man page for varargs (bsd section 3)

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VARARGS(3)									       VARARGS(3)

NAME
       varargs - variable argument list

SYNOPSIS
       #include <varargs.h>

       function(va_alist)
       va_dcl
       va_list pvar;
       va_start(pvar);
       f = va_arg(pvar, type);
       va_end(pvar);

DESCRIPTION
       This  set  of  macros provides a means of writing portable procedures that accept variable
       argument lists.	Routines having variable argument lists (such as printf(3)) that  do  not
       use  varargs  are  inherently nonportable, since different machines use different argument
       passing conventions.

       va_alist is used in a function header to declare a variable argument list.

       va_dcl is a declaration for va_alist.  Note that there is no semicolon after va_dcl.

       va_list is a type which can be used for the variable pvar, which is used to  traverse  the
       list.  One such variable must always be declared.

       va_start(pvar) is called to initialize pvar to the beginning of the list.

       va_arg(pvar,  type) will return the next argument in the list pointed to by pvar.  Type is
       the type to which the expected argument will be converted when passed as an argument.   In
       standard  C,  arguments that are char or short should be accessed as int, unsigned char or
       unsigned short are converted to unsigned int, and float arguments are converted to double.
       Different types can be mixed, but it is up to the routine to know what type of argument is
       expected, since it cannot be determined at runtime.

       va_end(pvar) is used to finish up.

       Multiple traversals, each bracketed by va_start ...  va_end, are possible.

EXAMPLE
	    #include <varargs.h>
	    execl(va_alist)
	    va_dcl
	    {
		 va_list ap;
		 char *file;
		 char *args[100];
		 int argno = 0;

		 va_start(ap);
		 file = va_arg(ap, char *);
		 while (args[argno++] = va_arg(ap, char *))
		      ;
		 va_end(ap);
		 return execv(file, args);
	    }

BUGS
       It is up to the calling routine to determine how many arguments there are, since it is not
       possible  to determine this from the stack frame.  For example, execl passes a 0 to signal
       the end of the list.  Printf can tell how many arguments are supposed to be there  by  the
       format.

       The  macros  va_start  and  va_end may be arbitrarily complex; for example, va_start might
       contain an opening brace, which is closed by a  matching  brace	in  va_end.   Thus,  they
       should only be used where they could be placed within a single complex statement.

7th Edition				   May 15, 1986 			       VARARGS(3)
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