Thread: Reallocate CString on Heap

  1. #1
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    Reallocate CString on Heap

    Hi,

    I have created a CString as:

    Code:
    char* p = malloc(3);
    p[0] = '1'
    p[1] = '1'
    p[2] = '1'
    Now, I want to change the string to: "He"

    Code:
    char* p = "He"
    But this reallocates the pointer adress. How to go around this?

  2. #2
    and the hat of int overfl Salem's Avatar
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    Do this.

    strcpy(p,"He");
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
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    #I am stupid
    Thank you!

  4. #4
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    I think it'd be more illustrating to change the string manually at this stage.
    Code:
    #define NULL_TERMINATION 1
    #define STR_SIZE 3 + NULL_TERMINATION
    
    char *p = malloc(STR_SIZE * sizeof(*p));
    p[0] = '1';
    p[1] = '1';
    p[2] = '1';
    P[3] = 0;
    //How do we change the string to "he"?
    p[0] = 'h';
    p[1] = 'e'
    p[2] = 0; //Otherwise we end up with "he1"
    Note that by convention, all strings in c should end with a 0 (technically a '\0' or null character which is normally 0, but it might not be in some obscure platform) which marks the end of the string. Library functions like strlen expect that, and won't work well without it.
    Last edited by Dren; 1 Week Ago at 04:56 PM. Reason: Dereference p during sizeof operation
    printf("I'm a %s.\n", strrev("Dren"));

  5. #5
    and the hat of int overfl Salem's Avatar
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    > char *p = malloc(STR_SIZE * sizeof(*p));
    Oooh, watch out for that operator precedence.

    Always put ( ) around all your #define expressions.

    > (technically a '\0' or null character which is normally 0,
    The ISO standard says it's always 0 (see 5.2.1 Character sets)
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

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