If free() knows the length of my array, why can't I ask for it in my own code?

Posted by Chris Cooper on Stack Overflow See other posts from Stack Overflow or by Chris Cooper
Published on 2010-04-16T05:49:03Z Indexed on 2010/04/16 5:53 UTC
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Filed under:

c

|

malloc

|

memory

|

free

I know that it's a common convention to pass the length of dynamically allocated arrays to functions that manipulate them:

void initializeAndFree(int* anArray, int length);

int main(){
    int arrayLength = 0;
    scanf("%d", &arrayLength);
    int* myArray = (int*)malloc(sizeof(int)*arrayLength);

    initializeAndFree(myArray, arrayLength);
}

void initializeAndFree(int* anArray, int length){
    int i = 0;
    for (i = 0; i < length; i++) {
        anArray[i] = 0;
    }
    free(anArray);
}

but if there's no way for me to get the length of the allocated memory from a pointer, how does free() "automagically" know what to deallocate? Why can't I get in on the magic, as a C programmer?

Where does free() get its free (har-har) knowledge from?

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If free() knows the length of my array, why can't I ask for it in my own code? - Developer IT

If free() knows the length of my array, why can't I ask for it in my own code?

c

malloc

memory

free

Related posts about c

Related posts about malloc

Malloc corrupting already malloc'd memory in C

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