Can I rewind a string like I can a file?

This is a discussion on Can I rewind a string like I can a file? within the C Programming forums, part of the General Programming Boards category; Think about this. printf, sprintf, and fprintf all work on streams , right? Just like scanf, sscanf, and fscanf work ...

  1. #1
    Third Eye Babkockdood's Avatar
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    Can I rewind a string like I can a file?

    Think about this. printf, sprintf, and fprintf all work on streams, right? Just like scanf, sscanf, and fscanf work on streams?

    When I use a function like rewind() or fseek() with SEEK_END, it changes where the stream position is, it changes where fprintf begins outputting, and where sscanf begins inputting.

    So, since strings are streams, like files are, can I rewind a string like I can a file?

    I guess I could write my string to a file and then use fscanf as a last resort, but I'm just wondering if there's an easier way. How would I go about writing a function like this myself?
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  2. #2
    - - - - - - - - oogabooga's Avatar
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    Give it a go and post some code. It would be pointless to write it to a file, so don't do that!

    BTW, C++ has a stringstream class.
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    Quote Originally Posted by Babkockdood View Post
    Think about this. printf, sprintf, and fprintf all work on streams, right? Just like scanf, sscanf, and fscanf work on streams?

    When I use a function like rewind() or fseek() with SEEK_END, it changes where the stream position is, it changes where fprintf begins outputting, and where sscanf begins inputting.

    So, since strings are streams, like files are, can I rewind a string like I can a file?

    I guess I could write my string to a file and then use fscanf as a last resort, but I'm just wondering if there's an easier way. How would I go about writing a function like this myself?
    To rewind a string all you have to do is put it back some where between where it is and the start of the string;

    Code:
    char buff[1024]; 
    char *b = buff;
    int      x;
    x = sprintf(b,"hello world %ld\n", (long)time(NULL));
    if(x <= 0)
      return;
    b += x ;
    x = sprintf(b,"hello world %d\n", b - buff);
    if(x <= 0)
      return;
    b += x;
    /*** to rewind the string pointed to by b  ***/
    b = buff;
    x = sprintf(b,"hello world %d\n", b - buff);
    if(x <= 0)
      return;
    /** will print "hello world 0\n" ***/
    printf("%s\n", buff);

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