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NAME
strtok, strtok_r — split string into tokens
SYNOPSIS
#include <string.h>
char *strtok(char *restrict s1, const char *restrict s2);
char *strtok_r(char *restrict s, const char *restrict sep,
char **restrict lasts);
DESCRIPTION
For strtok(): The functionality described on this reference page is aligned with the ISO C
standard. Any conflict between the requirements described here and the ISO C standard is
unintentional. This volume of POSIX.1‐2008 defers to the ISO C standard.
A sequence of calls to strtok() breaks the string pointed to by s1 into a sequence of
tokens, each of which is delimited by a byte from the string pointed to by s2. The first
call in the sequence has s1 as its first argument, and is followed by calls with a null
pointer as their first argument. The separator string pointed to by s2 may be different
from call to call.
The first call in the sequence searches the string pointed to by s1 for the first byte
that is not contained in the current separator string pointed to by s2. If no such byte
is found, then there are no tokens in the string pointed to by s1 and strtok() shall
return a null pointer. If such a byte is found, it is the start of the first token.
The strtok() function then searches from there for a byte that is contained in the current
separator string. If no such byte is found, the current token extends to the end of the
string pointed to by s1, and subsequent searches for a token shall return a null pointer.
If such a byte is found, it is overwritten by a NUL character, which terminates the
current token. The strtok() function saves a pointer to the following byte, from which the
next search for a token shall start.
Each subsequent call, with a null pointer as the value of the first argument, starts
searching from the saved pointer and behaves as described above.
The implementation shall behave as if no function defined in this volume of POSIX.1‐2008
calls strtok().
The strtok() function need not be thread-safe.
The strtok_r() function considers the null-terminated string s as a sequence of zero or
more text tokens separated by spans of one or more characters from the separator string
sep. The argument lasts points to a user-provided pointer which points to stored
information necessary for strtok_r() to continue scanning the same string.
In the first call to strtok_r(), s points to a null-terminated string, sep to a null-
terminated string of separator characters, and the value pointed to by lasts is ignored.
The strtok_r() function shall return a pointer to the first character of the first token,
write a null character into s immediately following the returned token, and update the
pointer to which lasts points.
In subsequent calls, s is a null pointer and lasts shall be unchanged from the previous
call so that subsequent calls shall move through the string s, returning successive tokens
until no tokens remain. The separator string sep may be different from call to call. When
no token remains in s, a null pointer shall be returned.
RETURN VALUE
Upon successful completion, strtok() shall return a pointer to the first byte of a token.
Otherwise, if there is no token, strtok() shall return a null pointer.
The strtok_r() function shall return a pointer to the token found, or a null pointer when
no token is found.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
Searching for Word Separators
The following example searches for tokens separated by <space> characters.
#include <string.h>
...
char *token;
char line[] = "LINE TO BE SEPARATED";
char *search = " ";
/* Token will point to "LINE". */
token = strtok(line, search);
/* Token will point to "TO". */
token = strtok(NULL, search);
Find First two Fields in a Buffer
The following example uses strtok() to find two character strings (a key and data
associated with that key) separated by any combination of <space>, <tab>, or <newline>
characters at the start of the array of characters pointed to by buffer.
#include <string.h>
...
char *buffer;
...
struct element {
char *key;
char *data;
} e;
...
// Load the buffer...
...
// Get the key and its data...
e.key = strtok(buffer, " \t\n");
e.data = strtok(NULL, " \t\n");
// Process the rest of the contents of the buffer...
...
APPLICATION USAGE
The strtok_r() function is thread-safe and stores its state in a user-supplied buffer
instead of possibly using a static data area that may be overwritten by an unrelated call
from another thread.
RATIONALE
The strtok() function searches for a separator string within a larger string. It returns a
pointer to the last substring between separator strings. This function uses static
storage to keep track of the current string position between calls. The new function,
strtok_r(), takes an additional argument, lasts, to keep track of the current position in
the string.
FUTURE DIRECTIONS
None.
SEE ALSO
The Base Definitions volume of POSIX.1‐2008, <string.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any
discrepancy between this version and the original IEEE and The Open Group Standard, the
original IEEE and The Open Group Standard is the referee document. The original Standard
can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .