August 11, 2002 STRTOK 3

### NAME

strtok,strtok_r - string tokens

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```char``*` strtok(```char * restrict str``, const char * restrict sep`)
```char``*` strtok_r(```char *str``, const char *sep``, char **lasts`)

### DESCRIPTION

The strtok(``) function is used to isolate sequential tokens in a nul-terminated string, ```str`. These tokens are separated in the string by at least one of the characters in ```sep`. The first time that strtok(``) is called, ```str` should be specified; subsequent calls, wishing to obtain further tokens from the same string, should pass a null pointer instead. The separator string, ```sep`, must be supplied each time, and may change between calls.

The strtok(``) function returns a pointer to the beginning of each subsequent token in the string, after replacing the separator character itself with a ```NUL` character. Separator characters at the beginning of the string or at the continuation point are skipped so that zero length tokens are not returned. When no more tokens remain, a null pointer is returned.

The strtok_r(``) function implements the functionality of strtok(``) but is passed an additional argument, ```lasts`, which points to a user-provided pointer which is used by strtok_r(``) to store state which needs to be kept between calls to scan the same string; unlike strtok(``), it is not necessary to limit tokenizing to a single string at a time when using strtok_r(``).

### EXAMPLES

The following will construct an array of pointers to each individual word in the string s:

  `

      #define MAXTOKENS       128

      char s[512], *p, *tokens[MAXTOKENS];
      char *last;
      int i = 0;

      snprintf(s, sizeof(s), "cat dog horse cow");

      for ((p = strtok_r(s, " ", &last)); p;
          (p = strtok_r(NULL, " ", &last)), i++) {
              if (i < MAXTOKENS - 1)
                      tokens[i] = p;
      }
      tokens[i] = NULL;

  `

That is, ```tokens[0]` will point to "cat, ```tokens[1]` will point to "dog, ```tokens[2]` will point to "horse, and ```tokens[3]` will point to "cow.

### SEE ALSO

index(3), memchr(3), rindex(3), strchr(3), strcspn(3), strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3)

### STANDARDS

The strtok(``) function conforms to ANSI X3.159-1989 (``ANSI C89'') . The strtok_r(``) function conforms to IEEE Std 1003.1c-1995 (``POSIX.1'') .

### BUGS

The System V strtok(``), if handed a string containing only delimiter characters, will not alter the next starting point, so that a call to strtok(``) with a different (or empty) delimiter string may return a non-```NULL` value. Since this implementation always alters the next starting point, such a sequence of calls would always return ```NULL`.