How to use realloc in a function in C

Question

Building on what I learned here: Manipulating dynamic array through functions in C.

void test(int data[])
{
    data[0] = 1;    
}    

int main(void)
{    
         


        

Answer 1

Keep in mind the difference between a pointer and an array.
An array is a chuck of memory in the stack, and that's all.If you have an array:

int arr[100];

Then arr is an address of memory, but also &arr is an adress of memory, and that address of memory is constant, not stored in any location.So you cannot say arr=NULL, since arr is not a variable that points to something.It's just a symbolic address: the address of where the array starts.Instead a pointer has it's own memory and can point to memory addresses.

It's enough that you change int[] to int*.
Also, variables are passed by copy so you need to pass an int** to the function.

About how using realloc, all the didactic examples include this:

1. Use realloc;
2. Check if it's NULL.In this case use perror and exit the program;
3. If it's not NULL use the memory allocated;
4. Free the memory when you don't need it anymore.

So that would be a nice example:

int* chuck= (int*) realloc (NULL, 10*sizeof(int)); // Acts like malloc,
              // casting is optional but I'd suggest it for readability
assert(chuck);
for(unsigned int i=0; i<10; i++)
{
    chunk[i]=i*10;
    printf("%d",chunk[i]);
}
free(chunk);