/* Compile with:
export CFLAGS="-g -Wall -O3"  #the usual.
export CC=c99
make conststruct
*/
#include <assert.h>
#include <stdlib.h>

typedef struct {
    int *counter1, *counter2;
} counter_s;

void check_counter(int *ctr){ assert(*ctr !=0); }

double ratio(counter_s const *in){
    check_counter(in->counter2);
    return *in->counter1/(*in->counter2+0.0);
}

int main(){
    counter_s cc = {.counter1=malloc(sizeof(int)),
                   .counter2=malloc(sizeof(int))};
    *cc.counter1 = *cc.counter2 = 1;
    ratio(&cc);
}