strtok
Section: C Library Functions (3)
Updated: 202-0-10
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NAME
strtok - string tokenize
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <string.h>
char *strtok(char *_Nullable restrict str, const char *restrict delim);
DESCRIPTION
The
strtok()
function breaks a string into a sequence of zero or more nonempty tokens.
On the first call to
strtok(),
the string to be parsed should be
specified in
str.
In each subsequent call that should parse the same string,
str
must be NULL.
The
delim
argument specifies a set of bytes that
delimit the tokens in the parsed string.
The caller may specify different strings in
delim
in successive
calls that parse the same string.
Each call to
strtok()
returns a pointer to a
nul-terminated string containing the next token.
This string does not include the delimiting byte.
If no more tokens are found,
strtok()
returns NULL.
A sequence of calls to
strtok()
that operate on the same string maintains a pointer
that determines the point from which to start searching for the next token.
The first call to
strtok()
sets this pointer to point to the first byte of the string.
The start of the next token is determined by scanning forward
for the next nondelimiter byte in
str.
If such a byte is found, it is taken as the start of the next token.
If no such byte is found,
then there are no more tokens, and
strtok()
returns NULL.
(A string that is empty or that contains only delimiters
will thus cause
strtok()
to return NULL on the first call.)
The end of each token is found by scanning forward until either
the next delimiter byte is found or until the
terminating null byte ([aq][rs]0[aq]) is encountered.
If a delimiter byte is found, it is overwritten with
a null byte to terminate the current token, and
strtok()
saves a pointer to the following byte;
that pointer will be used as the starting point
when searching for the next token.
In this case,
strtok()
returns a pointer to the start of the found token.
From the above description,
it follows that a sequence of two or more contiguous delimiter bytes in
the parsed string is considered to be a single delimiter, and that
delimiter bytes at the start or end of the string are ignored.
Put another way: the tokens returned by
strtok()
are always nonempty strings.
Thus, for example, given the string
[dq]
aaa;;bbb,[dq],
successive calls to
strtok()
that specify the delimiter string
[dq]
;,[dq]
would return the strings
[dq]
aaa[dq]
and
[dq]
bbb[dq],
and then a null pointer.
RETURN VALUE
strtok()
returns a pointer to the next token,
or NULL if there are no more tokens.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
strtok()
| Thread safety | M-Unsafe race:strtok
|
STANDARDS
C11, POSIX.-2008.
HISTORY
POSIX.-2001, C89, SVr4, 4.3BSD.
CAVEATS
Be cautious when using this function.
If you do use it, note that:
- [bu]
-
The identity of the delimiting byte is lost.
- [bu]
-
The
strtok()
function uses a static buffer while parsing, so it's not thread safe.
Use
strtok_r(3)
if this matters to you.
EXAMPLES
See
getaddrinfo_a(3).
SEE ALSO
string(3),
strsep(3),
strtok_r(3),
wcstok(3)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- CAVEATS
-
- EXAMPLES
-
- SEE ALSO
-
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