Defined in header <string.h> | ||
---|---|---|
(1) | ||
char *strtok( char *str, const char *delim ); | (until C99) | |
char *strtok( char *restrict str, const char *restrict delim ); | (since C99) | |
char *strtok_s(char *restrict str, rsize_t *restrict strmax, const char *restrict delim, char **restrict ptr); | (2) | (since C11) |
1) Finds the next token in a null-terminated byte string pointed to by
str
. The separator characters are identified by null-terminated byte string pointed to by delim
. This function is designed to be called multiples times to obtain successive tokens from the same string.
- If
str != NULL
, the call is treated as the first call tostrtok
for this particular string. The function searches for the first character which is not contained indelim
. - If no such character was found, there are no tokens in
str
at all, and the function returns a null pointer. - If such character was found, it is the beginning of the token. The function then searches from that point on for the first character that is contained in
delim
.- If no such character was found,
str
has only one token, and future calls tostrtok
will return a null pointer - If such character was found, it is replaced by the null character
'\0'
and the pointer to the following character is stored in a static location for subsequent invocations.
- If no such character was found,
- The function then returns the pointer to the beginning of the token
- If
str == NULL
, the call is treated as a subsequent calls tostrtok
: the function continues from where it left in previous invocation. The behavior is the same as if the previously stored pointer is passed asstr
.
The behavior is undefined if either
str
or delim
is not a pointer to a null-terminated byte string. 2) Same as (1), except that on every step, writes the number of characters left to see in
str
into *strmax
and writes the tokenizer's internal state to *ptr
. Repeat calls (with null str
) must pass strmax
and ptr
with the values stored by the previous call. Also, the following errors are detected at runtime and call the currently installed constraint handler function, without storing anything in the object pointed to by ptr
-
strmax
,delim
, orptr
is a null pointer - on a non-initial call (with null
str
),*ptr
is a null pointer - on the first call,
*strmax
is zero or greater thanRSIZE_MAX
- search for the end of a token reaches the end of the source string (as measured by the initial value of
*strmax
)) without encountering the null terminator
The behavior is undefined if both
str
points to a character array which lacks the null character and strmax
points to a value which is greater than the size of that character array. As all bounds-checked functions, strtok_s
is only guaranteed to be available if __STDC_LIB_EXT1__
is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__
to the integer constant 1
before including string.h
. Parameters
str | - | pointer to the null-terminated byte string to tokenize |
delim | - | pointer to the null-terminated byte string identifying delimiters |
strmax | - | pointer to an object which initially holds the size of str : strtok_s stores the number of characters that remain to be examined |
ptr | - | pointer to an object of type char* , which is used by strtok_s to store its internal state |
Return value
Returns pointer to the beginning of the next token or NULL
if there are no more tokens.
Note
This function is destructive: it writes the '\0'
characters in the elements of the string str
. In particular, a string literal cannot be used as the first argument of strtok
.
Each call to strtok
modifies a static variable: is not thread safe.
Unlike most other tokenizers, the delimiters in strtok
can be different for each subsequent token, and can even depend on the contents of the previous tokens.
The strtok_s
function differs from the POSIX strtok_r function by guarding against storing outside of the string being tokenized, and by checking runtime constraints.
Example
#define __STDC_WANT_LIB_EXT1__ 1 #include <string.h> #include <stdio.h> int main(void) { char input[] = "A bird came down the walk"; printf("Parsing the input string '%s'\n", input); char *token = strtok(input, " "); while(token) { puts(token); token = strtok(NULL, " "); } printf("Contents of the input string now: '"); for(size_t n = 0; n < sizeof input; ++n) input[n] ? printf("%c", input[n]) : printf("\\0"); puts("'"); #ifdef __STDC_LIB_EXT1__ char str[] = "A bird came down the walk"; rsize_t strmax = sizeof str; const char *delim = " "; char *next_token; printf("Parsing the input string '%s'\n", str); token = strtok_s(str, &strmax, delim, &next_token); while(token) { puts(token); token = strtok_s(NULL, &strmax, delim, &next_token); } printf("Contents of the input string now: '"); for(size_t n = 0; n < sizeof str; ++n) str[n] ? printf("%c", str[n]) : printf("\\0"); puts("'"); #endif }
Possible output:
Parsing the input string 'A bird came down the walk' A bird came down the walk Contents of the input string now: 'A\0bird\0came\0down\0the\0walk\0' Parsing the input string 'A bird came down the walk' A bird came down the walk Contents of the input string now: 'A\0bird\0came\0down\0the\0walk\0'
References
- C11 standard (ISO/IEC 9899:2011):
- 7.24.5.8 The strtok function (p: 369-370)
- K.3.7.3.1 The strtok_s function (p: 620-621)
- C99 standard (ISO/IEC 9899:1999):
- 7.21.5.8 The strtok function (p: 332-333)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.11.5.8 The strtok function
See also
finds the first location of any character in one string, in another string (function) | |
returns the length of the maximum initial segment that consists of only the characters not found in another byte string (function) | |
returns the length of the maximum initial segment that consists of only the characters found in another byte string (function) | |
(C95)(C11) | finds the next token in a wide string (function) |
C++ documentation for strtok |
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