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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 .