CODEWITHSUNDEEP
carraysdynamic
user2135885
user2135885

Reputation: 79

realloc and free

    double * copyTemp=NULL;
    double * output= malloc(sizeof(double*)*MallSize);
    double test1[] = {1.2,2.2,3.1};
    double test2[]={ 0.1,0.2,0.3,0.5,0.7,1.1,1.2,2.2};
    int i=0;
    int j=0;
    addArrayInOrder(test1 ,test2,output , &counter,&i , &j,size1,size2);
    ShrinkMemory ( MallSize,  counter, output ,  copyTemp );
    free(output); <- this part crashes for some reason
    return 0;

the problem I am getting is that sometime when i call free the program cashes. I dont see any mistake in this code since I set temp to NULL already so only one thing is pointed to the array is the ans pointer. So I should be able to call free at the end of the program to release the memory.

The function looks like 

void addArrayInOrder(double *array1, double *array2, double *final, int *finalCounter, int *arry1Counter, int *array2Counter, int ArrSize1, int ArrSize2)
{

    while (*arry1Counter < ArrSize1 && *array2Counter < ArrSize2)
    {

        if (isEqual(array1, array2, *arry1Counter, *array2Counter))
        {

            *(final + *finalCounter) = *(array1 + *arry1Counter);

            arry1Counter++;
            (*array2Counter)++;
            (*finalCounter)++;;
        }
        else if (*(array1 + *arry1Counter) > *(array2 + *array2Counter))
        {

            *(final + *finalCounter) = *(array2 + *array2Counter);
            (*array2Counter)++;
            (*finalCounter)++;
        }
        else
        {
            *(final + *finalCounter) = *(array1 + *arry1Counter);
            (*arry1Counter)++;
            (*finalCounter)++;
        }
    }

}
int ShrinkMemory(int MaxSize, int MinSize, double *final, double *temp)
{
    if (MaxSize != MinSize)
    {
        temp = realloc(final, MinSize * sizeof(double *));
        if (temp == NULL)
        {
            printf("relloc failed ! exixting /n");
            return 1;
        }
        else
        {

            printf("fsafda %p \n",temp);
            printf("fsafda %p \n",final);
            final=temp;
            temp=NULL;
            printf("fsafda %p \n",temp);
            printf("fsafda %p \n",final);
        }
    }
    return 0;
}

why is it crashing? I even printed out the memory using prinf %p and the address looks right

Upvotes: 0

Views: 102

Answers (2)

Dave
Dave

Reputation: 46249

You reassign final within ShrinkMemory and expect that to change what happens outside the function. C doesn't work like that. You need to use a double pointer (double **final) and change every reference to final to *final.

Also to be clear, a "double pointer" in this case means a pointer to a pointer to something (the 2 asterisks specify that); the type of thing being pointed to has nothing to do with it (by coincidence it's a "double" datatype here)

Upvotes: 2

Kerrek SB
Kerrek SB

Reputation: 476940

For an array of doubles, you want:

double * output= malloc(sizeof(double) * MallSize);
//                      ^^^^^^^^^^^^^^

(Likewise for realloc etc.)

Upvotes: 3

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