Flip words in a char array.

This is a discussion on Flip words in a char array. within the C Programming forums, part of the General Programming Boards category; Code: char *y=calloc(1,strlen(s)+1); char *p=s+strlen(s); You dint check the return value of calloc and dont really see the point of ...

  1. #16
    Registered User ssharish2005's Avatar
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    Code:
    char *y=calloc(1,strlen(s)+1);
    char *p=s+strlen(s);
    You dint check the return value of calloc and dont really see the point of this
    Code:
    if( !strchr(delims,*s) )
        strcat(y,s);
    ssharish
    Life is like riding a bicycle. To keep your balance you must keep moving - Einstein

  2. #17
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    What's the difference between calloc and malloc?

  3. #18
    Registered User ssharish2005's Avatar
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    Quote Originally Posted by mherald81 View Post
    What's the difference between calloc and malloc?
    calloc - allocated the memory and initialises the allocated memory to 0
    malloc - allocated memory but dosn't initialise the allocated memory

    ssharish
    Life is like riding a bicycle. To keep your balance you must keep moving - Einstein

  4. #19
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    Quote Originally Posted by ssharish2005 View Post
    calloc - allocated the memory and initialises the allocated memory to 0
    malloc - allocated memory but dosn't initialise the allocated memory

    ssharish
    Thanks. I can see why that would be useful for this program.

  5. #20
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    Can you explain this loop a bit for me?

    Code:
      while( p!=s )
        if( strchr(delims,*--p) )
          strcat(y,p+1),strncat(y,p,1),*p=0;
    It's mainly the strcat line that I'm lost on because all of that is on one line with a comma separating them. Thanks.

  6. #21
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by mherald81
    It's mainly the strcat line that I'm lost on because all of that is on one line with a comma separating them.
    That is just a (misguided) attempt to make the code more concise. It could have been written as:
    Code:
    char *wordrev(char *s, const char *delims)
    {
        char *y = calloc(1, strlen(s) + 1);
        char *p = s + strlen(s);
        while (p != s)
        {
            if (strchr(delims, *--p))
            {
                strcat(y, p + 1);
                strncat(y, p, 1);
                *p = 0;
            }
        }
        if (!strchr(delims, *s))
        {
            strcat(y, s);
        }
        strcpy(s, y);
        free(y);
        return s;
    }
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  7. #22
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    Quote Originally Posted by laserlight View Post
    That is just a (misguided) attempt to make the code more concise. It could have been written as:
    Code:
    char *wordrev(char *s, const char *delims)
    {
        char *y = calloc(1, strlen(s) + 1);
        char *p = s + strlen(s);
        while (p != s)
        {
            if (strchr(delims, *--p))
            {
                strcat(y, p + 1);
                strncat(y, p, 1);
                *p = 0;
            }
        }
        if (!strchr(delims, *s))
        {
            strcat(y, s);
        }
        strcpy(s, y);
        free(y);
        return s;
    }
    So strcat(y, p+1) concatenates without the space at the beginning of p and strncat(y,p,1) concatenates the space at the end. And *p=0 sets where p is pointing to in memory to 0? And the loop will continue until p and s are pointing at the same address in memory?
    Last edited by mherald81; 10-17-2010 at 09:24 AM.

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