#include <string.h>
char *strtok(char *restrict str, const char *restrict delim);
char *strtok_r(char *restrict str, const char *restrict delim,
char **restrict saveptr);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
strtok_r():
_POSIX_C_SOURCE
|| /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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 null-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 ('\0') 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 "aaa;;bbb,", successive calls to strtok() that specify the delimiter string ";," would return the strings "aaa" and "bbb", and then a null pointer.
The strtok_r() function is a reentrant version of strtok(). The saveptr argument is a pointer to a char * variable that is used internally by strtok_r() in order to maintain context between successive calls that parse the same string.
On the first call to strtok_r(), str should point to the string to be parsed, and the value of *saveptr is ignored (but see NOTES). In subsequent calls, str should be NULL, and saveptr (and the buffer that it points to) should be unchanged since the previous call.
Different strings may be parsed concurrently using sequences of calls to strtok_r() that specify different saveptr arguments.
| Interface | Attribute | Value |
| strtok() | Thread safety | MT-Unsafe race:strtok |
| strtok_r() | Thread safety | MT-Safe |
An example of the output produced by this program is the following:
$ ./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/'
1: a/bbb///cc
--> a
--> bbb
--> cc
2: xxx
--> xxx
3: yyy
--> yyy
int
main(int argc, char *argv[])
{
char *str1, *str2, *token, *subtoken;
char *saveptr1, *saveptr2;
if (argc != 4) {
fprintf(stderr, "Usage: %s string delim subdelim\n",
argv[0]);
exit(EXIT_FAILURE);
}
for (int j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
token = strtok_r(str1, argv[2], &saveptr1);
if (token == NULL)
break;
printf("%d: %s\n", j, token);
for (str2 = token; ; str2 = NULL) {
subtoken = strtok_r(str2, argv[3], &saveptr2);
if (subtoken == NULL)
break;
printf(" --> %s\n", subtoken);
}
}
exit(EXIT_SUCCESS);
}
Another example program using strtok() can be found in getaddrinfo_a(3).