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| 15daeeaf | 1 | .\" @(#)stdarg.3 6.1 (Berkeley) %G% |
| 41a44cfa | 2 | .\" |
| 15daeeaf | 3 | .TH VARARGS 3 "" |
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4 | .AT 3 |
| 5 | .SH NAME | |
| 6 | varargs \- variable argument list | |
| 7 | .SH SYNOPSIS | |
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8 | .B "#include <varargs.h>" |
| 9 | .PP | |
| 10 | .I function\c | |
| 11 | .RB ( va_alist ) | |
| 12 | .br | |
| 13 | .B va_dcl | |
| 14 | .br | |
| 15 | .B va_list | |
| 16 | .IR pvar ; | |
| 17 | .br | |
| 18 | .B va_start\c | |
| 19 | .RI ( pvar ); | |
| 20 | .br | |
| 21 | f = | |
| 22 | .B va_arg\c | |
| 23 | .RI ( pvar , | |
| 24 | .IR type ); | |
| 25 | .br | |
| 26 | .B va_end\c | |
| 27 | .RI ( pvar ); | |
| 41a44cfa | 28 | .SH DESCRIPTION |
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29 | This set of macros provides a means of writing portable procedures that |
| 30 | accept variable argument lists. | |
| 31 | Routines having variable argument lists (such as | |
| 32 | .IR printf (3)) | |
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33 | that do not use varargs are inherently nonportable, since different |
| 34 | machines use different argument passing conventions. | |
| 35 | .PP | |
| 36 | .B va_alist | |
| 37 | is used in a function header to declare a variable argument list. | |
| 38 | .PP | |
| 39 | .B va_dcl | |
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40 | is a declaration for |
| 41 | .BR va_alist . | |
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42 | Note that there is no semicolon after |
| 43 | .B va_dcl. | |
| 44 | .PP | |
| 45 | .B va_list | |
| 46 | is a type which can be used for the variable | |
| 4d575989 | 47 | .IR pvar , |
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48 | which is used to traverse the list. |
| 49 | One such variable must always be declared. | |
| 50 | .PP | |
| 4d575989 | 51 | .B va_start\c |
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52 | .RI (pvar) |
| 53 | is called to initialize | |
| 54 | .I pvar | |
| 55 | to the beginning of the list. | |
| 56 | .PP | |
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57 | .B va_arg\c |
| 58 | .RI ( pvar , | |
| 59 | .IR type ) | |
| 60 | will return the next argument in the list pointed to by | |
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61 | .IR pvar . |
| 62 | .I Type | |
| 63 | is the type the argument is expected to be. | |
| 64 | Different types can be mixed, but it is up | |
| 65 | to the routine to know what type of argument is | |
| 66 | expected, since it cannot be determined at runtime. | |
| 67 | .PP | |
| 4d575989 | 68 | .B va_end\c |
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69 | .RI ( pvar ) |
| 70 | is used to finish up. | |
| 71 | .PP | |
| 4d575989 | 72 | Multiple traversals, each bracketed by |
| 41a44cfa | 73 | .B va_start |
| 4d575989 | 74 | \&... |
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75 | .B va_end, |
| 76 | are possible. | |
| 77 | .SH EXAMPLE | |
| 78 | .nf | |
| 79 | \fB#include\fP <varargs.h> | |
| 80 | execl(\fBva_alist\fP) | |
| 81 | \fBva_dcl\fP | |
| 82 | { | |
| 83 | \fBva_list\fP ap; | |
| 84 | \fBchar\fP *file; | |
| 85 | \fBchar\fP *args[100]; | |
| 86 | \fBint\fP argno = 0; | |
| 87 | ||
| 88 | \fBva_start\fP(ap); | |
| 89 | file = \fBva_arg(ap, \fBchar\fP *); | |
| 90 | \fBwhile\fP (args[argno++] = \fBva_arg\fP(ap, \fBchar\fP *)) | |
| 91 | \fB;\fP | |
| 92 | \fBva_end\fP(ap); | |
| 93 | \fBreturn\fP execv(file, args); | |
| 94 | } | |
| 95 | .fi | |
| 96 | .SH BUGS | |
| 97 | It is up to the calling routine to determine how many arguments | |
| 98 | there are, since it is not possible to determine this from the | |
| 99 | stack frame. For example, | |
| 100 | .I execl | |
| 101 | passes a 0 to signal the end of the list. | |
| 102 | .I Printf | |
| 4d575989 | 103 | can tell how many arguments are supposed to be there by the format. |