1STRTOK(3)                  Linux Programmer's Manual                 STRTOK(3)
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NAME

6       strtok, strtok_r - extract tokens from strings
7

SYNOPSIS

9       #include <string.h>
10
11       char *strtok(char *str, const char *delim);
12
13       char *strtok_r(char *str, const char *delim, char **saveptr);
14
15   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
16
17       strtok_r(): _POSIX_C_SOURCE
18           || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
19

DESCRIPTION

21       The  strtok()  function breaks a string into a sequence of zero or more
22       nonempty tokens.  On the first call  to  strtok(),  the  string  to  be
23       parsed should be specified in str.  In each subsequent call that should
24       parse the same string, str must be NULL.
25
26       The delim argument specifies a set of bytes that delimit the tokens  in
27       the  parsed  string.  The caller may specify different strings in delim
28       in successive calls that parse the same string.
29
30       Each call to strtok() returns a pointer  to  a  null-terminated  string
31       containing the next token.  This string does not include the delimiting
32       byte.  If no more tokens are found, strtok() returns NULL.
33
34       A sequence of calls to strtok() that operate on the same  string  main‐
35       tains a pointer that determines the point from which to start searching
36       for the next token.  The first call to strtok() sets  this  pointer  to
37       point  to the first byte of the string.  The start of the next token is
38       determined by scanning forward for the next nondelimiter byte  in  str.
39       If  such  a  byte is found, it is taken as the start of the next token.
40       If no such byte is found, then there are no more tokens,  and  strtok()
41       returns NULL.  (A string that is empty or that contains only delimiters
42       will thus cause strtok() to return NULL on the first call.)
43
44       The end of each token is found by scanning  forward  until  either  the
45       next  delimiter byte is found or until the terminating null byte ('\0')
46       is encountered.  If a delimiter byte is found, it is overwritten with a
47       null  byte to terminate the current token, and strtok() saves a pointer
48       to the following byte; that pointer will be used as the starting  point
49       when  searching  for  the next token.  In this case, strtok() returns a
50       pointer to the start of the found token.
51
52       From the above description, it follows that a sequence of two  or  more
53       contiguous  delimiter  bytes in the parsed string is considered to be a
54       single delimiter, and that delimiter bytes at the start or end  of  the
55       string  are  ignored.  Put another way: the tokens returned by strtok()
56       are always nonempty strings.   Thus,  for  example,  given  the  string
57       "aaa;;bbb,",  successive  calls  to strtok() that specify the delimiter
58       string ";," would return the strings "aaa" and "bbb", and then  a  null
59       pointer.
60
61       The  strtok_r()  function is a reentrant version strtok().  The saveptr
62       argument is a pointer to a char * variable that is used  internally  by
63       strtok_r()  in  order to maintain context between successive calls that
64       parse the same string.
65
66       On the first call to strtok_r(), str should point to the string  to  be
67       parsed,  and the value of saveptr is ignored.  In subsequent calls, str
68       should be NULL, and saveptr should  be  unchanged  since  the  previous
69       call.
70
71       Different  strings  may be parsed concurrently using sequences of calls
72       to strtok_r() that specify different saveptr arguments.
73

RETURN VALUE

75       The strtok() and strtok_r() functions return  a  pointer  to  the  next
76       token, or NULL if there are no more tokens.
77

ATTRIBUTES

79       For   an   explanation   of   the  terms  used  in  this  section,  see
80       attributes(7).
81
82       ┌───────────┬───────────────┬───────────────────────┐
83Interface  Attribute     Value                 
84       ├───────────┼───────────────┼───────────────────────┤
85strtok()   │ Thread safety │ MT-Unsafe race:strtok │
86       ├───────────┼───────────────┼───────────────────────┤
87strtok_r() │ Thread safety │ MT-Safe               │
88       └───────────┴───────────────┴───────────────────────┘

CONFORMING TO

90       strtok()
91              POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
92
93       strtok_r()
94              POSIX.1-2001, POSIX.1-2008.
95

BUGS

97       Be cautious when using these functions.  If you do use them, note that:
98
99       * These functions modify their first argument.
100
101       * These functions cannot be used on constant strings.
102
103       * The identity of the delimiting byte is lost.
104
105       * The strtok() function uses a static buffer while parsing, so it's not
106         thread safe.  Use strtok_r() if this matters to you.
107

EXAMPLE

109       The  program  below uses nested loops that employ strtok_r() to break a
110       string into a two-level hierarchy of tokens.   The  first  command-line
111       argument specifies the string to be parsed.  The second argument speci‐
112       fies the delimiter byte(s) to be used  to  separate  that  string  into
113       "major"  tokens.  The third argument specifies the delimiter byte(s) to
114       be used to separate the "major" tokens into subtokens.
115
116       An example of the output produced by this program is the following:
117
118           $ ./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/'
119           1: a/bbb///cc
120                    --> a
121                    --> bbb
122                    --> cc
123           2: xxx
124                    --> xxx
125           3: yyy
126                    --> yyy
127
128   Program source
129
130       #include <stdio.h>
131       #include <stdlib.h>
132       #include <string.h>
133
134       int
135       main(int argc, char *argv[])
136       {
137           char *str1, *str2, *token, *subtoken;
138           char *saveptr1, *saveptr2;
139           int j;
140
141           if (argc != 4) {
142               fprintf(stderr, "Usage: %s string delim subdelim\n",
143                       argv[0]);
144               exit(EXIT_FAILURE);
145           }
146
147           for (j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
148               token = strtok_r(str1, argv[2], &saveptr1);
149               if (token == NULL)
150                   break;
151               printf("%d: %s\n", j, token);
152
153               for (str2 = token; ; str2 = NULL) {
154                   subtoken = strtok_r(str2, argv[3], &saveptr2);
155                   if (subtoken == NULL)
156                       break;
157                   printf(" --> %s\n", subtoken);
158               }
159           }
160
161           exit(EXIT_SUCCESS);
162       }
163
164       Another  example  program  using  strtok()  can  be  found  in   getad‐
165       drinfo_a(3).
166

SEE ALSO

168       index(3),   memchr(3),  rindex(3),  strchr(3),  string(3),  strpbrk(3),
169       strsep(3), strspn(3), strstr(3), wcstok(3)
170

COLOPHON

172       This page is part of release 4.16 of the Linux  man-pages  project.   A
173       description  of  the project, information about reporting bugs, and the
174       latest    version    of    this    page,    can     be     found     at
175       https://www.kernel.org/doc/man-pages/.
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179GNU                               2017-09-15                         STRTOK(3)
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