strtok giving empty strings

This is a discussion on strtok giving empty strings within the C Programming forums, part of the General Programming Boards category; Hello everyone, I am having a bit of trouble getting strtok to tokenize my string. Here is the bit of ...

  1. #1
    Registered User TheBigH's Avatar
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    strtok giving empty strings

    Hello everyone,
    I am having a bit of trouble getting strtok to tokenize my string. Here is the bit of code that is giving me trouble:
    Code:
      printf( "%s\n", temp );
      strcpy(h, strtok( temp, ":" ));
      strcpy(m, strtok( NULL, ":" ));
      strcpy(s, strtok( NULL, ":" ));
      printf( "%s,%s,%s\n",h, m, s );
    What comes out is this:
    Code:
    14:30:20.555
    14,,20.555
    That is, the first and third of the three substrings work perfectly but the middle one gives me an empty string when what I want is the "30".

    Why is it doing that, and how do I fix it?
    Thanks,
    H.

  2. #2
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    My output is 14,30,20.555. Are you sure that you've recompiled your code???

  3. #3
    Registered User claudiu's Avatar
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    Can you post the entire code?
    1. Get rid of gets(). Never ever ever use it again. Replace it with fgets() and use that instead.
    2. Get rid of void main and replace it with int main(void) and return 0 at the end of the function.
    3. Get rid of conio.h and other antiquated DOS crap headers.
    4. Don't cast the return value of malloc, even if you always always always make sure that stdlib.h is included.

  4. #4
    Registered User TheBigH's Avatar
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    Sure, here is the entirety of my code

    Code:
    #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    
    int main(void){
    
      char temp[]="14:30:20.555";
      char   h[3];
      char   m[3];
      char   s[6];
        
      printf( "%s\n", temp );
      strcpy(h, strtok( temp, ":" ));
      strcpy(m, strtok( NULL, ":" ));
      strcpy(s, strtok( NULL, ":" ));
      printf( "%s,%s,%s\n",h, m, s );
    
      return 0;
    }

  5. #5
    C++ Witch laserlight's Avatar
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    I cannot duplicate the problem, but I do note that s should have a size of 7 instead of 6.
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    char s[6]; /* 20.555 has 6 chars & no room for null byte declaring to 7 work @ least for me */

  7. #7
    Registered User TheBigH's Avatar
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    Aha! That fixed it. How stupid of me. Why a missing \0 at the end of the third substring should affect the second, I'm not sure.

    Thanks everyone.

  8. #8
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by TheBigH
    Why a missing \0 at the end of the third substring should affect the second, I'm not sure.
    One possibility is that that the position of s is before that of m in memory. strtok() writes to m, and then to s. But due to the lack of space for the null terminator, there is buffer overflow, and the null terminator is written to m[0], thus turning m into an empty string.
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  9. #9
    Registered User TheBigH's Avatar
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    That makes a lot of sense, and would explain why you couldn't replicate the error: it's essentially random where the character arrays are stored so your m and s might have been in the other order.

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