Problem allocating memory.

This is a discussion on Problem allocating memory. within the C Programming forums, part of the General Programming Boards category; I'm having a problem with my app, it crashes when I try to allocate some memory. What I use to ...

  1. #1
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    Question Problem allocating memory.

    I'm having a problem with my app, it crashes when I try to allocate some memory. What I use to allocate the memory is
    Code:
    entpairs[i].key = (char*) (MAX_ENTITY_KEYLENGTH*sizeof(char));
    entpairs is defined as a entpairs_t
    Code:
    typedef struct
    {
    	char *key;
    	char *val;
    } entpairs_t;
    and MAX_ENTITY_KEYLENGTH is
    Code:
    #define MAX_ENTITY_KEYLENGTH	64
    Is there something wrong with my code?

  2. #2
    pronounced 'fib' FillYourBrain's Avatar
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    You aren't allocating anything. All you are doing is a cast of the value:

    MAX_ENTITY_KEYLENGTH*sizeof(char)

    to char*

    That's not allocation. Look up malloc() and calloc()
    "You are stupid! You are stupid! Oh, and don't forget, you are STUPID!" - Dexter

  3. #3
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    Originally posted by FillYourBrain
    You aren't allocating anything. All you are doing is a cast of the value:

    MAX_ENTITY_KEYLENGTH*sizeof(char)

    to char*

    That's not allocation. Look up malloc() and calloc()
    Haha, I forgot to add the malloc, the line should be
    Code:
    entpairs[i].key = (char*) malloc(MAX_ENTITY_KEYLENGTH*sizeof(char));
    THANKS FillYourBrain.

  4. #4
    Code Goddess Prelude's Avatar
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    >entpairs[i].key = (char*) malloc(MAX_ENTITY_KEYLENGTH*sizeof(char));
    The cast isn't needed for malloc and can hide errors if you forget to include stdlib.h. Also, sizeof ( char ) is redundant as it will always be 1. This would be better:
    Code:
    entpairs[i].key = malloc(MAX_ENTITY_KEYLENGTH);
    Of course, an explicit sizeof for char arrays is often used to force the type of the expression to size_t. This is done by overly anal programmers...such as myself. The following is the preferred method for doing this as it doesn't rely on the type of pointer you are allocating memory to:
    Code:
    entpairs[i].key = malloc(MAX_ENTITY_KEYLENGTH * sizeof *entpairs[i].key);
    My best code is written with the delete key.

  5. #5
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    Analysis of the allocation statement:

    Code:
    entpairs[i].key = (char*) malloc(MAX_ENTITY_KEYLENGTH*sizeof(char));
    In the code above, i don't think there can be anything wrong to the right hand side of the statement. so possible errors in the left hand side of the statement are,

    1) value of ' i ' goes out of array bound.

    2) If ' i ' isn't out of bound index then is entpairs[i] allocated memory?

    -Give more Information about your code.

    Thanks

  6. #6
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    Originally posted by doraiashok
    Analysis of the allocation statement:

    Code:
    entpairs[i].key = (char*) malloc(MAX_ENTITY_KEYLENGTH*sizeof(char));
    In the code above, i don't think there can be anything wrong to the right hand side of the statement. so possible errors in the left hand side of the statement are,

    1) value of ' i ' goes out of array bound.

    2) If ' i ' isn't out of bound index then is entpairs[i] allocated memory?

    -Give more Information about your code.

    Thanks
    The problem is fixed, for some reason I forgot to add the malloc so it wasn't doing anything as FillYourBrain pointed to me. So everything works, thanks anyway.

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