STRTOK(3P) POSIX Programmer's Manual STRTOK(3P)
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This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult 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 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 con-
tained 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 vol-
ume 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 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 charac-
ter 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 sepa-
rator 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>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 <new-
line>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, Copyright (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.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 STRTOK(3P)
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