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ComputingCString.h

strtok_r

String tokens
+ View other versions (3)

Interface

#include <string.h>
char strtok (char *str, const char *sep)
char strtok_r (char *str, const char *sep, char **last)

Description

The strtok function is used to isolate sequential tokens in a null-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 implementation will behave as if no library function calls strtok.

The strtok_r function is a reentrant version of strtok. The context pointer last must be provided on each call. The strtok_r function may also be used to nest two parsing loops within one another, as long as separate context pointers are used. The strtok and strtok_r functions return a pointer to the beginning of each subsequent token in the string, after replacing the token itself with a NUL character. When no more tokens remain, a null pointer is returned.

Example:

Example - String tokens
Problem
The following uses strtok_r to parse two strings using separate contexts:

Workings
char test[80], blah[80];
char *sep = "\\/:;=-";
char *word, *phrase, *brkt, *brkb;
 
strcpy(test, "This;is.a:test:of=the/string\\tokenizer-function.");
 
for (word = strtok_r(test, sep, &brkt);
     word;
     word = strtok_r(NULL, sep, &brkt))
{
    strcpy(blah, "blah:blat:blab:blag");
 
    for (phrase = strtok_r(blah, sep, &brkb); 
           phrase; 
           phrase = strtok_r(NULL, sep, &brkb))
    {
        printf("So far we're at %s:%s\n", word, phrase);
    }
}

Standards

The strtok function conforms to ISO/IEC 9899:1990 ("ISO C90").

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.