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Top Forums Programming Make sure strtok_r() function Post 302883907 by yifangt on Thursday 16th of January 2014 03:51:42 PM
Old 01-16-2014
Yes, your code worked perfectly and much simpler. The only thing bugs me is the NULL for the second strtok_r():
Quote:
word=strtok_r(string1, sep, &tmp1);
word=strtok_r(NULL, sep, &tmp1); // NULL means 'continue from last token'.
Swallowing it without digestion bothers me a lot. I was thinking this way according to the explanation:
Quote:
char *strtok_r(char *restrict s, const char *restrict sep, char **restrict lasts);
In the first call to strtok_r(), s points to a null-terminated string, sep to a null-terminated string of separator characters, and the value pointed to by lasts is ignored. The strtok_r() function shall return a pointer to the first character of the first token, write a null character into s immediately following the returned token, and update the pointer to which lasts points. In subsequent calls, s is a NULL pointer and lasts shall be unchanged from the previous call so that subsequent calls shall move through the string s, returning successive tokens until no tokens remain. The separator string sep may be different from call to call. When no token remains in s, a NULL pointer shall be returned.
:
Code:
word=strtok_r(ptr, sep, &tmp1))    //pop one token from the beginning, rest (&tmp1) is the left_over
ptr = tmp1;                      //move the pointer to the beginning of the rest (&tmp1)

But not sure, especially without the new pointer ptr. It seems I have to just remember and use it in your way. Trying more to get the prototype of strtok_r(), and to understand reentrancy, a related concept new to me. I hate C but I love it more.
Ok, MUST follow the usage of the function as migurus said:
Code:
...... on the first  call the 1st argument should point to the input string, then on the  following calls it (1st argument) should be NULL.


Last edited by yifangt; 01-16-2014 at 05:50 PM..
 

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STRTOK(3)						   BSD Library Functions Manual 						 STRTOK(3)

NAME
strtok, strtok_r -- string tokens LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <string.h> char * strtok(char *str, const char *sep); char * strtok_r(char *str, const char *sep, char **last); DESCRIPTION
This interface is obsoleted by strsep(3). 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. EXAMPLES
The following uses strtok_r() to parse two strings using separate contexts: 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 ", word, phrase); } } SEE ALSO
memchr(3), strchr(3), strcspn(3), strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3), wcstok(3) STANDARDS
The strtok() function conforms to ISO/IEC 9899:1990 (``ISO C90''). AUTHORS
Wes Peters <wes@softweyr.com>, Softweyr LLC Based on the FreeBSD 3.0 implementation. 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. BSD
November 27, 1998 BSD
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