1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
|
'\" t
.\" Copyright (C) 2005, 2013 Michael Kerrisk <mtk.manpages@gmail.com>
.\" a few fragments from an earlier (1996) version by
.\" Andries Brouwer (aeb@cwi.nl) remain.
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" Rewritten old page, 960210, aeb@cwi.nl
.\" Updated, added strtok_r. 2000-02-13 Nicolás Lichtmaier <nick@debian.org>
.\" 2005-11-17, mtk: Substantial parts rewritten
.\" 2013-05-19, mtk: added much further detail on the operation of strtok()
.\"
.TH strtok 3 2023-10-31 "Linux man-pages 6.06"
.SH NAME
strtok, strtok_r \- extract tokens from strings
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <string.h>
.P
.BI "char *strtok(char *restrict " str ", const char *restrict " delim );
.BI "char *strtok_r(char *restrict " str ", const char *restrict " delim ,
.BI " char **restrict " saveptr );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR strtok_r ():
.nf
_POSIX_C_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
The
.BR strtok ()
function breaks a string into a sequence of zero or more nonempty tokens.
On the first call to
.BR strtok (),
the string to be parsed should be
specified in
.IR str .
In each subsequent call that should parse the same string,
.I str
must be NULL.
.P
The
.I delim
argument specifies a set of bytes that
delimit the tokens in the parsed string.
The caller may specify different strings in
.I delim
in successive
calls that parse the same string.
.P
Each call to
.BR strtok ()
returns a pointer to a
null-terminated string containing the next token.
This string does not include the delimiting byte.
If no more tokens are found,
.BR strtok ()
returns NULL.
.P
A sequence of calls to
.BR strtok ()
that operate on the same string maintains a pointer
that determines the point from which to start searching for the next token.
The first call to
.BR strtok ()
sets this pointer to point to the first byte of the string.
The start of the next token is determined by scanning forward
for the next nondelimiter byte in
.IR str .
If such a byte is found, it is taken as the start of the next token.
If no such byte is found,
then there are no more tokens, and
.BR strtok ()
returns NULL.
(A string that is empty or that contains only delimiters
will thus cause
.BR strtok ()
to return NULL on the first call.)
.P
The end of each token is found by scanning forward until either
the next delimiter byte is found or until the
terminating null byte (\[aq]\e0\[aq]) is encountered.
If a delimiter byte is found, it is overwritten with
a null byte to terminate the current token, and
.BR strtok ()
saves a pointer to the following byte;
that pointer will be used as the starting point
when searching for the next token.
In this case,
.BR strtok ()
returns a pointer to the start of the found token.
.P
From the above description,
it follows that a sequence of two or more contiguous delimiter bytes in
the parsed string is considered to be a single delimiter, and that
delimiter bytes at the start or end of the string are ignored.
Put another way: the tokens returned by
.BR strtok ()
are always nonempty strings.
Thus, for example, given the string "\fIaaa;;bbb,\fP",
successive calls to
.BR strtok ()
that specify the delimiter string "\fI;,\fP"
would return the strings "\fIaaa\fP" and "\fIbbb\fP",
and then a null pointer.
.P
The
.BR strtok_r ()
function is a reentrant version of
.BR strtok ().
The
.I saveptr
argument is a pointer to a
.I char\~*
variable that is used internally by
.BR strtok_r ()
in order to maintain context between successive calls that parse the
same string.
.P
On the first call to
.BR strtok_r (),
.I str
should point to the string to be parsed, and the value of
.I *saveptr
is ignored (but see NOTES).
In subsequent calls,
.I str
should be NULL, and
.I saveptr
(and the buffer that it points to)
should be unchanged since the previous call.
.P
Different strings may be parsed concurrently using sequences of calls to
.BR strtok_r ()
that specify different
.I saveptr
arguments.
.SH RETURN VALUE
The
.BR strtok ()
and
.BR strtok_r ()
functions return a pointer to
the next token, or NULL if there are no more tokens.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR strtok ()
T} Thread safety MT-Unsafe race:strtok
T{
.na
.nh
.BR strtok_r ()
T} Thread safety MT-Safe
.TE
.SH VERSIONS
On some implementations,
.\" Tru64, according to its manual page
.I *saveptr
is required to be NULL on the first call to
.BR strtok_r ()
that is being used to parse
.IR str .
.SH STANDARDS
.TP
.BR strtok ()
C11, POSIX.1-2008.
.TP
.BR strtok_r ()
POSIX.1-2008.
.SH HISTORY
.TP
.BR strtok ()
POSIX.1-2001, C89, SVr4, 4.3BSD.
.TP
.BR strtok_r ()
POSIX.1-2001.
.SH BUGS
Be cautious when using these functions.
If you do use them, note that:
.IP \[bu] 3
These functions modify their first argument.
.IP \[bu]
These functions cannot be used on constant strings.
.IP \[bu]
The identity of the delimiting byte is lost.
.IP \[bu]
The
.BR strtok ()
function uses a static buffer while parsing, so it's not thread safe.
Use
.BR strtok_r ()
if this matters to you.
.SH EXAMPLES
The program below uses nested loops that employ
.BR strtok_r ()
to break a string into a two-level hierarchy of tokens.
The first command-line argument specifies the string to be parsed.
The second argument specifies the delimiter byte(s)
to be used to separate that string into "major" tokens.
The third argument specifies the delimiter byte(s)
to be used to separate the "major" tokens into subtokens.
.P
An example of the output produced by this program is the following:
.P
.in +4n
.EX
.RB "$" " ./a.out \[aq]a/bbb///cc;xxx:yyy:\[aq] \[aq]:;\[aq] \[aq]/\[aq]"
1: a/bbb///cc
\-\-> a
\-\-> bbb
\-\-> cc
2: xxx
\-\-> xxx
3: yyy
\-\-> yyy
.EE
.in
.SS Program source
\&
.\" SRC BEGIN (strtok.c)
.EX
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
\&
int
main(int argc, char *argv[])
{
char *str1, *str2, *token, *subtoken;
char *saveptr1, *saveptr2;
int j;
\&
if (argc != 4) {
fprintf(stderr, "Usage: %s string delim subdelim\en",
argv[0]);
exit(EXIT_FAILURE);
}
\&
for (j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
token = strtok_r(str1, argv[2], &saveptr1);
if (token == NULL)
break;
printf("%d: %s\en", j, token);
\&
for (str2 = token; ; str2 = NULL) {
subtoken = strtok_r(str2, argv[3], &saveptr2);
if (subtoken == NULL)
break;
printf("\et \-\-> %s\en", subtoken);
}
}
\&
exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.P
Another example program using
.BR strtok ()
can be found in
.BR getaddrinfo_a (3).
.SH SEE ALSO
.BR memchr (3),
.BR strchr (3),
.BR string (3),
.BR strpbrk (3),
.BR strsep (3),
.BR strspn (3),
.BR strstr (3),
.BR wcstok (3)
|