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  of strtok().  The
62       saveptr argument is a pointer to a char * variable that is used  inter‐
63       nally  by  strtok_r()  in  order to maintain context between successive
64       calls that 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 (but see NOTES).  In sub‐
68       sequent calls, str should be NULL, and saveptr (and the buffer that  it
69       points to) should be unchanged since the previous 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  to‐
76       ken, or NULL if there are no more tokens.
77

ATTRIBUTES

79       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
80       tributes(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

NOTES

97       On some implementations, *saveptr is required to be NULL on  the  first
98       call to strtok_r() that is being used to parse str.
99

BUGS

101       Be cautious when using these functions.  If you do use them, note that:
102
103       * These functions modify their first argument.
104
105       * These functions cannot be used on constant strings.
106
107       * The identity of the delimiting byte is lost.
108
109       * The strtok() function uses a static buffer while parsing, so it's not
110         thread safe.  Use strtok_r() if this matters to you.
111

EXAMPLES

113       The program below uses nested loops that employ strtok_r() to  break  a
114       string  into  a  two-level hierarchy of tokens.  The first command-line
115       argument specifies the string to be parsed.  The second argument speci‐
116       fies the delimiter byte(s) to be used to separate that string into "ma‐
117       jor" tokens.  The third argument specifies the delimiter byte(s) to  be
118       used to separate the "major" tokens into subtokens.
119
120       An example of the output produced by this program is the following:
121
122           $ ./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/'
123           1: a/bbb///cc
124                    --> a
125                    --> bbb
126                    --> cc
127           2: xxx
128                    --> xxx
129           3: yyy
130                    --> yyy
131
132   Program source
133
134       #include <stdio.h>
135       #include <stdlib.h>
136       #include <string.h>
137
138       int
139       main(int argc, char *argv[])
140       {
141           char *str1, *str2, *token, *subtoken;
142           char *saveptr1, *saveptr2;
143
144           if (argc != 4) {
145               fprintf(stderr, "Usage: %s string delim subdelim\n",
146                       argv[0]);
147               exit(EXIT_FAILURE);
148           }
149
150           for (int j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
151               token = strtok_r(str1, argv[2], &saveptr1);
152               if (token == NULL)
153                   break;
154               printf("%d: %s\n", j, token);
155
156               for (str2 = token; ; str2 = NULL) {
157                   subtoken = strtok_r(str2, argv[3], &saveptr2);
158                   if (subtoken == NULL)
159                       break;
160                   printf(" --> %s\n", subtoken);
161               }
162           }
163
164           exit(EXIT_SUCCESS);
165       }
166
167       Another   example  program  using  strtok()  can  be  found  in  getad‐
168       drinfo_a(3).
169

SEE ALSO

171       index(3),  memchr(3),  rindex(3),  strchr(3),  string(3),   strpbrk(3),
172       strsep(3), strspn(3), strstr(3), wcstok(3)
173

COLOPHON

175       This  page  is  part of release 5.10 of the Linux man-pages project.  A
176       description of the project, information about reporting bugs,  and  the
177       latest     version     of     this    page,    can    be    found    at
178       https://www.kernel.org/doc/man-pages/.
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182GNU                               2020-11-01                         STRTOK(3)
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