Question

Possible Duplicate:
How can I get the size of an array from a pointer in C?
How can I get the size of a memory block allocated using malloc()?

void func( int *p)
{
      // Add code to print MEMORY SIZE which is pointed by pointer p.
}
int main()
{
      int *p = (int *) malloc(10 * sizeof(int));
      func(p);
}

How can we find MEMORY SIZE from memory pointer P in func() ?

Answer 1

You cannot do this in a portable manner in C. It may not be stored anywhere; malloc() could reserve a region much larger than you asked for, and isn’t guaranteed to store any information about how much your requested.

You either need to use a standard size, such as malloc(ARRAY_LEN * sizeof(int)) or malloc(sizeof mystruct), or you need to pass the information around with the pointer:

struct integers {
    size_t count;
    int *p;
};

void fun(integers ints) {
    // use ints.count to find out how many items we have
}

int main() {
    struct integers ints;
    ints.count = 10;
    ints.p = malloc(ints.count * sizeof(int));
    fun(ints);
}