GMP, C language memory allocation and pointer

Question

I was trying to code something like this

....
mpz_class *x = NULL;
mpz_class *lValue = NULL;
....
for(int k = 0; k < 2; k++) {
    x = NULL;
    lValue = NULL;
    x = (mpz_class*) malloc(sizeof(mpz_class) * exponentForFactors[k]);
    lValue = (mpz_class*) malloc(sizeof(mpz_class) * exponentForFactors[k]);

    rValue = 0;

    mpz_class exp = (p-1)/q[k];

    mpz_powm(lValue[0].get_mpz_t(), B.get_mpz_t(),exp.get_mpz_t(), p.get_mpz_t()); <- this part

exponentForFactors[k] = {3, 1} this code will loop twice as k is less than 2. At first loop, it is ok. there is no error but when it is the second loop, it has this error message where I pointed. malloc: *** error for object 0x6000000000000000: pointer being realloc'd was not allocated *** set a breakpoint in malloc_error_break to debug

I do not understand why this thing takes place only at the second loop? Any suggestion would be grateful. Thanks.

////////////////////////////

even this code(when the second loop)

cout << "lvalue = " << lValue[0] << endl;

has the problem.

Answer 1

Since mpz_class is a class, and you are clearly coding in C++ (not C, I have changed your language tag accordingly), using the C allocator is improper. You should instead use new[] or better yet, use std::vector<> to allocate your array. Although you have allocated memory for your arrays, the objects within them are uninitialized, because their constructors have not been called.