1STRTOK(3) Linux Programmer's Manual STRTOK(3)
2
6 strtok, strtok_r - extract tokens from strings
7
9 #include <string.h>
10 char *strtok(char *restrict str, const char *restrict delim);
12 char *strtok_r(char *restrict str, const char *restrict delim,
13 char **restrict saveptr);
14 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
16 strtok_r():
18 _POSIX_C_SOURCE
19 || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
20
22 The strtok() function breaks a string into a sequence of zero or more
23 nonempty tokens. On the first call to strtok(), the string to be
24 parsed should be specified in str. In each subsequent call that should
25 parse the same string, str must be NULL.
26 The delim argument specifies a set of bytes that delimit the tokens in
28 the parsed string. The caller may specify different strings in delim
29 in successive calls that parse the same string.
30 Each call to strtok() returns a pointer to a null-terminated string
32 containing the next token. This string does not include the delimiting
33 byte. If no more tokens are found, strtok() returns NULL.
34 A sequence of calls to strtok() that operate on the same string main‐
36 tains a pointer that determines the point from which to start searching
37 for the next token. The first call to strtok() sets this pointer to
38 point to the first byte of the string. The start of the next token is
39 determined by scanning forward for the next nondelimiter byte in str.
40 If such a byte is found, it is taken as the start of the next token.
41 If no such byte is found, then there are no more tokens, and strtok()
42 returns NULL. (A string that is empty or that contains only delimiters
43 will thus cause strtok() to return NULL on the first call.)
44 The end of each token is found by scanning forward until either the
46 next delimiter byte is found or until the terminating null byte ('\0')
47 is encountered. If a delimiter byte is found, it is overwritten with a
48 null byte to terminate the current token, and strtok() saves a pointer
49 to the following byte; that pointer will be used as the starting point
50 when searching for the next token. In this case, strtok() returns a
51 pointer to the start of the found token.
52 From the above description, it follows that a sequence of two or more
54 contiguous delimiter bytes in the parsed string is considered to be a
55 single delimiter, and that delimiter bytes at the start or end of the
56 string are ignored. Put another way: the tokens returned by strtok()
57 are always nonempty strings. Thus, for example, given the string
58 "aaa;;bbb,", successive calls to strtok() that specify the delimiter
59 string ";," would return the strings "aaa" and "bbb", and then a null
60 pointer.
61 The strtok_r() function is a reentrant version of strtok(). The
63 saveptr argument is a pointer to a char * variable that is used inter‐
64 nally by strtok_r() in order to maintain context between successive
65 calls that parse the same string.
66 On the first call to strtok_r(), str should point to the string to be
68 parsed, and the value of *saveptr is ignored (but see NOTES). In sub‐
69 sequent calls, str should be NULL, and saveptr (and the buffer that it
70 points to) should be unchanged since the previous call.
71 Different strings may be parsed concurrently using sequences of calls
73 to strtok_r() that specify different saveptr arguments.
74
76 The strtok() and strtok_r() functions return a pointer to the next to‐
77 ken, or NULL if there are no more tokens.
78
80 For an explanation of the terms used in this section, see at‐
81 tributes(7).
82 ┌──────────────────────────────┬───────────────┬───────────────────────┐
84 │Interface │ Attribute │ Value │
85 ├──────────────────────────────┼───────────────┼───────────────────────┤
86 │strtok() │ Thread safety │ MT-Unsafe race:strtok │
87 ├──────────────────────────────┼───────────────┼───────────────────────┤
88 │strtok_r() │ Thread safety │ MT-Safe │
89 └──────────────────────────────┴───────────────┴───────────────────────┘
90
92 strtok()
93 POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
94 strtok_r()
96 POSIX.1-2001, POSIX.1-2008.
97
99 On some implementations, *saveptr is required to be NULL on the first
100 call to strtok_r() that is being used to parse str.
101
103 Be cautious when using these functions. If you do use them, note that:
104 * These functions modify their first argument.
106 * These functions cannot be used on constant strings.
108 * The identity of the delimiting byte is lost.
110 * The strtok() function uses a static buffer while parsing, so it's not
112 thread safe. Use strtok_r() if this matters to you.
113
115 The program below uses nested loops that employ strtok_r() to break a
116 string into a two-level hierarchy of tokens. The first command-line
117 argument specifies the string to be parsed. The second argument speci‐
118 fies the delimiter byte(s) to be used to separate that string into "ma‐
119 jor" tokens. The third argument specifies the delimiter byte(s) to be
120 used to separate the "major" tokens into subtokens.
121 An example of the output produced by this program is the following:
123 $ ./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/'
125 1: a/bbb///cc
126 --> a
127 --> bbb
128 --> cc
129 2: xxx
130 --> xxx
131 3: yyy
132 --> yyy
133 Program source
135 #include <stdio.h>
137 #include <stdlib.h>
138 #include <string.h>
139 int
141 main(int argc, char *argv[])
142 {
143 char *str1, *str2, *token, *subtoken;
144 char *saveptr1, *saveptr2;
145 if (argc != 4) {
147 fprintf(stderr, "Usage: %s string delim subdelim\n",
148 argv[0]);
149 exit(EXIT_FAILURE);
150 }
151 for (int j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
153 token = strtok_r(str1, argv[2], &saveptr1);
154 if (token == NULL)
155 break;
156 printf("%d: %s\n", j, token);
157 for (str2 = token; ; str2 = NULL) {
159 subtoken = strtok_r(str2, argv[3], &saveptr2);
160 if (subtoken == NULL)
161 break;
162 printf(" --> %s\n", subtoken);
163 }
164 }
165 exit(EXIT_SUCCESS);
167 }
168 Another example program using strtok() can be found in getad‐
170 drinfo_a(3).
171
173 index(3), memchr(3), rindex(3), strchr(3), string(3), strpbrk(3),
174 strsep(3), strspn(3), strstr(3), wcstok(3)
175
177 This page is part of release 5.13 of the Linux man-pages project. A
178 description of the project, information about reporting bugs, and the
179 latest version of this page, can be found at
180 https://www.kernel.org/doc/man-pages/.
181GNU 2021-03-22 STRTOK(3)