projects / unix-history / blame
| Commit | Line | Data |
|---|---|---|
| 41a44cfa KM |
1 | .\" @(#)stdarg.3 4.1 (Berkeley) %G% |
| 2 | .\" | |
| 3 | .TH VARARGS 3 | |
| 4 | .AT 3 | |
| 5 | .SH NAME | |
| 6 | varargs \- variable argument list | |
| 7 | .SH SYNOPSIS | |
| 8 | .nf | |
| 9 | #include <varargs.h> | |
| 10 | \fIfunction\fR(\fBva_alist\fR) | |
| 11 | \fBva_dcl | |
| 12 | va_list \fIpvar\fR; | |
| 13 | \fBva_start\fR(\fIpvar\fR); | |
| 14 | f = \fBva_arg\fR(\fIpvar\fR, \fItype\fR); | |
| 15 | \fBva_end\fR(\fIpvar\fR); | |
| 16 | .fi | |
| 17 | .SH DESCRIPTION | |
| 18 | This set of macros allows portable procedures that accept variable | |
| 19 | argument lists to be written. | |
| 20 | Routines which have variable argument lists (such as | |
| 21 | .IR printf(3)) | |
| 22 | that do not use varargs are inherently nonportable, since different | |
| 23 | machines use different argument passing conventions. | |
| 24 | .PP | |
| 25 | .B va_alist | |
| 26 | is used in a function header to declare a variable argument list. | |
| 27 | .PP | |
| 28 | .B va_dcl | |
| 29 | is a declaration for \fBva_alist\fP. | |
| 30 | Note that there is no semicolon after | |
| 31 | .B va_dcl. | |
| 32 | .PP | |
| 33 | .B va_list | |
| 34 | is a type which can be used for the variable | |
| 35 | .I pvar, | |
| 36 | which is used to traverse the list. | |
| 37 | One such variable must always be declared. | |
| 38 | .PP | |
| 39 | .B va_start | |
| 40 | .RI (pvar) | |
| 41 | is called to initialize | |
| 42 | .I pvar | |
| 43 | to the beginning of the list. | |
| 44 | .PP | |
| 45 | .B va_arg | |
| 46 | .RI ( pvar , type ) | |
| 47 | will return the next argument in the list | |
| 48 | pointed to by | |
| 49 | .IR pvar . | |
| 50 | .I Type | |
| 51 | is the type the argument is expected to be. | |
| 52 | Different types can be mixed, but it is up | |
| 53 | to the routine to know what type of argument is | |
| 54 | expected, since it cannot be determined at runtime. | |
| 55 | .PP | |
| 56 | .B va_end | |
| 57 | .RI ( pvar ) | |
| 58 | is used to finish up. | |
| 59 | .PP | |
| 60 | Multiple traversals, each bracketted by | |
| 61 | .B va_start | |
| 62 | \&.. | |
| 63 | .B va_end, | |
| 64 | are possible. | |
| 65 | .SH EXAMPLE | |
| 66 | .nf | |
| 67 | \fB#include\fP <varargs.h> | |
| 68 | execl(\fBva_alist\fP) | |
| 69 | \fBva_dcl\fP | |
| 70 | { | |
| 71 | \fBva_list\fP ap; | |
| 72 | \fBchar\fP *file; | |
| 73 | \fBchar\fP *args[100]; | |
| 74 | \fBint\fP argno = 0; | |
| 75 | ||
| 76 | \fBva_start\fP(ap); | |
| 77 | file = \fBva_arg(ap, \fBchar\fP *); | |
| 78 | \fBwhile\fP (args[argno++] = \fBva_arg\fP(ap, \fBchar\fP *)) | |
| 79 | \fB;\fP | |
| 80 | \fBva_end\fP(ap); | |
| 81 | \fBreturn\fP execv(file, args); | |
| 82 | } | |
| 83 | .fi | |
| 84 | .SH BUGS | |
| 85 | It is up to the calling routine to determine how many arguments | |
| 86 | there are, since it is not possible to determine this from the | |
| 87 | stack frame. For example, | |
| 88 | .I execl | |
| 89 | passes a 0 to signal the end of the list. | |
| 90 | .I Printf | |
| 91 | can tell how many arguments are there by the format. |