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1.1       root        1: .TH VARARGS 3  "19 January 1983"
                      2: .SH NAME
                      3: varargs \- variable argument list
                      4: .SH SYNOPSIS
                      5: .B "#include <varargs.h>"
                      6: .PP
                      7: .I function\c
                      8: .RB ( va_alist )
                      9: .br
                     10: .B va_dcl
                     11: .br
                     12: .B va_list
                     13: .IR pvar ;
                     14: .br
                     15: .B va_start\c
                     16: .RI ( pvar );
                     17: .br
                     18: f =
                     19: .B va_arg\c
                     20: .RI ( pvar ,
                     21: .IR type );
                     22: .br
                     23: .B va_end\c
                     24: .RI ( pvar );
                     25: .SH DESCRIPTION
                     26: This set of macros provides a means of writing portable procedures that
                     27: accept variable argument lists.
                     28: Routines having variable argument lists (such as
                     29: .IR printf (3))
                     30: that do not use varargs are inherently nonportable, since different
                     31: machines use different argument passing conventions.
                     32: .PP
                     33: .B va_alist
                     34: is used in a function header to declare a variable argument list.
                     35: .PP
                     36: .B va_dcl
                     37: is a declaration for
                     38: .BR va_alist .
                     39: Note that there is no semicolon after
                     40: .B va_dcl.
                     41: .PP
                     42: .B va_list
                     43: is a type which can be used for the variable
                     44: .IR pvar ,
                     45: which is used to traverse the list.
                     46: One such variable must always be declared.
                     47: .PP
                     48: .B va_start\c
                     49: .RI (pvar)
                     50: is called to initialize
                     51: .I pvar
                     52: to the beginning of the list.
                     53: .PP
                     54: .B va_arg\c
                     55: .RI ( pvar ,
                     56: .IR type )
1.1.1.2 ! root       57: returns the next argument in the list pointed to by
1.1       root       58: .IR pvar .
                     59: .I Type
                     60: is the type the argument is expected to be.
                     61: Different types can be mixed, but it is up
                     62: to the routine to know what type of argument is
                     63: expected, since it cannot be determined at runtime.
                     64: .PP
                     65: .B va_end\c
                     66: .RI ( pvar )
                     67: is used to finish up.
                     68: .PP
                     69: Multiple traversals, each bracketed by
                     70: .B va_start
                     71: \&...
                     72: .B va_end,
                     73: are possible.
                     74: .SH EXAMPLE
                     75: .nf
                     76:        \fB#include\fP <varargs.h>
                     77:        execl(\fBva_alist\fP)
                     78:        \fBva_dcl\fP
                     79:        {
                     80:                \fBva_list\fP ap;
                     81:                \fBchar\fP *file;
                     82:                \fBchar\fP *args[100];
                     83:                \fBint\fP argno = 0;
                     84: 
                     85:                \fBva_start\fP(ap);
                     86:                file = \fBva_arg(ap, \fBchar\fP *);
                     87:                \fBwhile\fP (args[argno++] = \fBva_arg\fP(ap, \fBchar\fP *))
                     88:                        \fB;\fP
                     89:                \fBva_end\fP(ap);
                     90:                \fBreturn\fP execv(file, args);
                     91:        }
                     92: .fi
                     93: .SH BUGS
                     94: It is up to the calling routine to determine how many arguments
                     95: there are, since it is not possible to determine this from the
                     96: stack frame.  For example,
                     97: .I execl
                     98: passes a 0 to signal the end of the list.
                     99: .I Printf
                    100: can tell how many arguments are supposed to be there by the format.

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