![[BACK]](/cvsweb/icons/back.gif){kind=icon}
Return to varargs.3 CVS log ![[TXT]](/cvsweb/icons/text.gif){kind=icon}
![[DIR]](/cvsweb/icons/dir.gif){kind=icon}
Up to [CSRG BSD Unix] / 43BSDReno / share / man / man3|
Return to varargs.3 CVS log | Up to [CSRG BSD Unix] / 43BSDReno / share / man / man3 |
1.1 root 1: .\" Copyright (c) 1990 The Regents of the University of California.
2: .\" All rights reserved.
3: .\"
4: .\" Redistribution and use in source and binary forms are permitted
5: .\" provided that: (1) source distributions retain this entire copyright
6: .\" notice and comment, and (2) distributions including binaries display
7: .\" the following acknowledgement: ``This product includes software
8: .\" developed by the University of California, Berkeley and its contributors''
9: .\" in the documentation or other materials provided with the distribution
10: .\" and in all advertising materials mentioning features or use of this
11: .\" software. Neither the name of the University nor the names of its
12: .\" contributors may be used to endorse or promote products derived
13: .\" from this software without specific prior written permission.
14: .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
15: .\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
16: .\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
17: .\"
18: .\" @(#)varargs.3 6.4 (Berkeley) 5/14/90
19: .\"
20: .TH VARARGS 3 "May 14, 1990"
21: .AT 3
22: .SH NAME
23: varargs \- variable argument lists
24: .SH SYNOPSIS
25: .nf
26: .ft B
27: #include <stdarg.h>
28:
29: void
30: va_start(va_list ap, last);
31:
32: type
33: va_arg(va_list ap, type);
34:
35: void
36: va_end(va_list ap);
37: .ft R
38: .fi
39: .SH DESCRIPTION
40: A function may be called with a varying number of arguments of varying
41: types.
42: The include file
43: .I <stdarg.h>
44: declares a type (\fIva_list\fP) and defines three macros for stepping
45: through a list of arguments whose number and types are not known to
46: the called function.
47: .PP
48: The called function must declare an object of type
49: .I va_list
50: which is used by the macros
51: .IR va_start ,
52: .IR va_arg ,
53: and
54: .IR va_end .
55: .PP
56: The
57: .I va_start
58: macro initializes
59: .I ap
60: for subsequent use by
61: .I va_arg
62: and
63: .IR va_end ,
64: and must be called first.
65: .PP
66: The parameter
67: .I last
68: is the name of the last parameter before the variable argument list,
69: i.e. the last parameter of which the calling function knows the type.
70: .PP
71: Because the address of this parameter is used in the
72: .I va_start
73: macro, it should not be declared as a register variable, or as a
74: function or array type.
75: .PP
76: The
77: .I va_start
78: macro returns no value.
79: .PP
80: The
81: .I va_arg
82: macro expands to an expression that has the type and value of the next
83: argument in the call.
84: The parameter
85: .I ap
86: is the
87: .I va_list ap
88: initialized by
89: .IR va_start .
90: Each call to
91: .I va_arg
92: modifies
93: .I ap
94: so that the next call returns the next argument.
95: The parameter
96: .I type
97: is a type name specified so that the type of a pointer to an
98: object that has the specified type can be obtained simply by
99: adding a
100: .I *
101: to
102: .IR type .
103: .PP
104: If there is no next argument, or if
105: .I type
106: is not compatible with the type of the actual next argument
107: (as promoted according to the default argument promotions),
108: random errors will occur.
109: .PP
110: The first use of the
111: .I va_arg
112: macro after that of the
113: .I va_start
114: macro returns the argument after
115: .IR last .
116: Successive invocations return the values of the remaining
117: arguments.
118: .PP
119: The
120: .I va_end
121: macro handles a normal return from the function whose variable argument
122: list was initialized by
123: .IR va_start .
124: .PP
125: The
126: .I va_end
127: macro returns no value.
128: .SH STANDARDS
129: The
130: .IR va_start ,
131: .IR va_arg ,
132: and
133: .I va_end
134: macros are ANSI C compatible.
135: .SH COMPATIBILITY
136: These macros are
137: .B not
138: compatible with the historic macros they replace.
139: A backward compatible version can be found in the include
140: file
141: .IR <varargs.h> .
142: .SH EXAMPLES
143: The function
144: .I foo
145: takes a string of format characters and prints out the argument
146: associated with each format character based on the type.
147: .sp
148: .nf
149: .RS
150: foo(fmt)
151: char *fmt;
152: {
153: va_list ap;
154: int d;
155: char c, *p, *s;
156:
157: va_start(ap, fmt);
158: while (*fmt)
159: switch(*fmt++) {
160: case 's': /* string */
161: s = va_arg(ap, char *);
162: printf("string %s\en", s);
163: break;
164: case 'd': /* int */
165: d = va_arg(ap, int);
166: printf("int %d\en", d);
167: break;
168: case 'c': /* char */
169: c = va_arg(ap, char);
170: printf("char %c\en", c);
171: break;
172: }
173: va_end(ap);
174: }
175: .fi
This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.