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| Commit | Line | Data |
|---|---|---|
| 19b14bf7 C |
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 ) | |
| 57 | will return the next argument in the list pointed to by | |
| 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. |