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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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STRTOK(3P) POSIX Programmer's Manual STRTOK(3P)
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.
strtok, strtok_r — split string into tokens
#include <string.h>
char *strtok(char *restrict s, const char *restrict sep);
char *strtok_r(char *restrict s, const char *restrict sep,
char **restrict state);
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.1‐2017 defers to the ISO C
standard.
A sequence of calls to strtok() breaks the string pointed to by s
into a sequence of tokens, each of which is delimited by a byte
from the string pointed to by sep. The first call in the sequence
has s as its first argument, and is followed by calls with a null
pointer as their first argument. The separator string pointed to
by sep may be different from call to call.
The first call in the sequence searches the string pointed to by s
for the first byte that is not contained in the current separator
string pointed to by sep. If no such byte is found, then there
are no tokens in the string pointed to by s 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 s, 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.1‐2017 calls strtok().
The strtok() function need not be thread-safe.
The strtok_r() function shall be equivalent to strtok(), except
that strtok_r() shall be thread-safe and the argument state points
to a user-provided pointer that allows strtok_r() to maintain
state between calls which scan the same string. The application
shall ensure that the pointer pointed to by state is unique for
each string (s) being processed concurrently by strtok_r() calls.
The application need not initialize the pointer pointed to by
state to any particular value. The implementation shall not update
the pointer pointed to by state to point (directly or indirectly)
to resources, other than within the string s, that need to be
freed or released by the caller.
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.
No errors are defined.
The following sections are informative.
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...
...
Note that if sep is the empty string, strtok() and strtok_r()
return a pointer to the remainder of the string being tokenized.
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.
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, state, to keep
track of the current position in the string.
None.
The Base Definitions volume of POSIX.1‐2017, string.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 .
IEEE/The Open Group 2017 STRTOK(3P)
Pages that refer to this page: string.h(0p), localeconv(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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