How do I determine the number of elements in an array?

Question

I just got some problems to determine the number of elements in one of my arrays. I got for example following code:

typedef struct
{
    char b[100];
    int c;
}abc;

typedef struct
{
    char qwe[50];
    abc *poi;
}def;

abc xyz[] = {
    {"xyz", 10},
    {"ijk", 20},
    {"gdf", 30},
    {"hfg", 40}
};

abc uio[] = {
    {"cde", 50},
    {"ghi", 60},
    {"hbc", 70}
};

def mnb[] = {
    {"kio", xyz},
    {"mkl", uio}
};

I know that I can determin the number of elements in the array mnb like this:

int count_mnb = sizeof(mnb) / sizeof(mnb[0]);

But how do I determine the number of elements in xyz? I want to use xyz as part of the first element of mnb and not just replace mnb by xzy. Something like this:

int count_xyz = sizeof(*mnb[0].poi) / sizeof();

But I couldn't figure how to do this.