while loop help

This is a discussion on while loop help within the C Programming forums, part of the General Programming Boards category; hi everyone i am just struggling a little on my while loops i want the loop to save the character ...

  1. #1
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    while loop help

    hi everyone

    i am just struggling a little on my while loops

    i want the loop to save the character so it can build up a name e.g.

    Code:
    char *pos = strchr(buffer, 'R');
    int posa = pos-buffer;
    while (buffer != posa)
          {
    this is where i have got now i want it so while it is not equal to posa ('R') then for it to store what the content of buffer currently is

    so buffer[0] might be f
    buffer [1] might be i
    buffer [2] might be l
    buffer [3] might be l
    buffer [4] might be R

    so now it will store the whole word 'fill'

    all replies are appreciated thanks

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    The word already is in buffer. Did you want it somewhere else? If so, strncpy will move things around.

  3. #3
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    buffer is a char * and posa is an integer. You can't compare them directly, and your compiler should be screaming about this. Turn on all the warnings when you compile and make sure they're all resolved.

    What you actually have is buffer pointing to some place in memory, say address 1000. pos is pointing to some place in buffer, the first location of an 'R', say address 1005. posa is then the difference of these two, or 5. This is effectively the length from the start of buffer to the 'R', but you don't really need this. Just do
    Code:
    while (buffer != pos) {
        ...
        buffer++;
    }
    Note you also fail to handle the case that there is no 'R' in buffer. strchr will return NULL and your program will seg fault.

  4. #4
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    ok so strncpy worked its wonders but now i need to add a null character on the end
    is there a way to do this without knowing the string length?
    i could have just done headname[5]='\0';
    but i do not completely know whether there are only 4, 5, 6, 45 characters.
    is there a way of pointing to the end of the string so i could add the null?

  5. #5
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    destination[posa] = '\0';

  6. #6
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    thank you for that damn you lot on here make c look like ... eating cake

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