Question

I have an array of pointer to struct, and for any reasons when I print this array, there is a spare element at the end of it, and thus causes the code to print a NULL byte at the end.

Is there anyway I can delete the last chunk of memory?

For example:

typedef struct
{
    char *name;
} B;

typedef struct
{
    B *var;
} A;

int main() {
    int num = 5; //for example
    A *foo = malloc(sizeof(A));
    B *bar = malloc(num * sizeof(B));
    for (int i = 0; i < num; i++) {
        bar[i] = *create_b(&bar[i]); // some function that works.
    }
    foo->var = bar;
    while (foo->var != NULL) {
        printf("This is %s\n",foo->var->name);
            foo->var++; 
    }
}

Everything is printed out just fine, but there’s an unwanted printing at the end of the loop. Something like:

This is A
This is B
This is C
This is D
This is F
This is

Apparently the array only has 5 elements, the last one prints nothing.

Answer 1

Your printing loop is:

foo->var = bar;
while (foo->var != NULL) {
    printf("This is %s\n",foo->var->name);
    foo->var++; 
}

But foo->var will never equal NULL, since you’re just incrementing a pointer, so you will eventually read past the end of the bar array and your application will probably crash.

If you replace the while loop with for (int i = 0; i < num; i++), it will print the correct number of elements.