Question

I need to identify a global struct (array), consisted of 4 integers.
The problem is, size of that struct array is not known in advance.

I’m trying to make sth. like this:

typedef struct
{
    int value;
    int MAXleft;
    int MAXright;
    int MAX;
} strnum;

int main ()
{
    int size;
    scanf("%d", &size);

    strnum numbers[size];

    return 0;
}

I heard that, it is possible to do this by pointers but I don’t know how to do.

Answer 1

You can allocate the space for several structures dynamically like this:

strnum *numbers = malloc( size * sizeof(strnum) );

Then you can use it like any regular array (mostly).

It might be more convenient to use calloc instead of malloc. It allocates a number of blocks and fills them with zeros. Please note, that malloc doesn’t clear allocated memory.

strnum *numbers = calloc( size, sizeof(strnum) );

When you are done with the memory don’t forget to call free( numbers ), which will return the allocated memory back to a memory manager.

If you don’t free it when it’s no longer required and allocate some more and more, a memory footprint of the program will grow for no good reason as the program continues to work. This is called a memory leak and should be avoided. It might eventually result in the lack of memory for a program and unpredictable results.

And don’t forget to include a stdlib.h header with prototypes of memory allocation functions.