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STRTOK(3P) POSIX Programmer's Manual STRTOK(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (con-
sult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on
Linux.
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 IEEE Std 1003.1-2001
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 cur-
rent 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 null byte, 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 IEEE Std 1003.1-2001 calls strtok().
The strtok() function need not be reentrant. A function that is not required to be reentrant is not required to 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 char-
acters, and the value pointed to by lasts is ignored. The strtok_r() function shall return a pointer to the first char-
acter 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 dif-
ferent 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>s.
#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);
Breaking a Line
The following example uses strtok() to break a line into two character strings separated by any combination of <space>s,
<tab>s, or <newline>s.
#include <string.h>
...
struct element {
char *key;
char *data;
};
...
char line[LINE_MAX];
char *key, *data;
...
key = strtok(line, " \n");
data = strtok(NULL, " \n");
...
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 IEEE Std 1003.1-2001, <string.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.open-
group.org/unix/online.html .
IEEE/The Open Group 2003 STRTOK(3P)
