#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);
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.
The strtok_r() function shall return a pointer to the token found, or a null pointer when no token is found.
The following sections are informative.
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);
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...
...
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.
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 .