Question

I’ve got a piece of code:

void Read(int T[], int len) {
    int i;
    T = (int*) malloc(len * sizeof *T);
    for (i=0;i<len;i++) {
        scanf("%d", &T[i]);
    }
}

I use in this way:

int *T;
Read(T,len);

Next, I wanna write my table:

void Write(int T[], int len) {
    int i;
    for(i=0;i<len;i++) {
        printf("%d, ", T[i]);
    }
    printf("\n");
    return;
}

And use it:

Write(T,len);   

It gives me wrong results. I almost sure that problem is connected with ‘&‘ but I cannot deal with it.

Thanks in advance

Answer 1

One problem may be that you’re modifying a local variable T inside your Read function:

int *T;
Read(T, len);
// ...

void Read(int T[], int len) {
    int i;
    T = (int*) malloc(len * sizeof *T);
    // ...
}

The T inside Read is a copy of the real T variable. You assign a new value to the copy, but the original remains unchanged.

To actually modify the outer T, pass a pointer to it like so:

int *T;
Read(&T, len);
// ...

void Read(int **T, int len) {
    int i;
    *T = (int*) malloc(len * sizeof *T);
    for (i=0;i<len;i++) {
        scanf("%d", &(*T)[i]);
    }
}