C++ Debugging Help Memory Leak - c++

Question

I am currently working on an assignment and I am struggling greatly with debugging my memory leak. My program runs and passes however, when I upload it for grading my code has a memory leak. If someone could point me in the right direction on how to fix it I would greatly appreciate!
I've tried everything I could think of!
#ifndef A2_HPP
#define A2_HPP
#include <algorithm>
class sorted_sc_array {
public:
/*
* return: none
* constructor with no argument assign size_ = 0 and ptr_ to null pointer
*/
sorted_sc_array() : size_(0), ptr_(nullptr) {
}
/*
* return: none
* destructor delete the pointer ptr_
*/
~sorted_sc_array() {
delete[] ptr_;
}
/*
* return: none
* when assign an object to new object
*/
sorted_sc_array(const sorted_sc_array& A){
const signed char* str = A.data();
int sz = A.size_;
this->size_ = 0;
for(int i = 0; i < sz; i++) this->insert(str[i]);
delete[] str;
}
/*
* return: sorted_sc_array
* overloading of operator =
*/
sorted_sc_array& operator=(const sorted_sc_array& A){
const signed char* str = A.data();
int sz = A.size_;
this->size_ = 0;
for(int i = 0; i < sz; i++) this->insert(str[i]);
}
/*
* return int
* return the size of the ptr_
*/
int size() const {
return size_;
}
/*
* return char*
* return the deta stored in the pointer ptr_
*/
const signed char* data() const {
return ptr_;
}
/*
* return void
* add new char to the pointer ptr_ and sort the the new string after the addition
*/
void insert(signed char c) {
signed char *str = (signed char*)malloc((size_ + 1)*sizeof(char));
for(int i = 0; i < size_; i++) str[i] = ptr_[i];
str[size_++] = c;
ptr_ = (signed char*)malloc((size_)*sizeof(char));
for(int i = 0; i < size_; i++) ptr_[i] = str[i];
std::sort(ptr_, ptr_ + size_);
delete[] str;
}
private:
int size_; // size of the array
signed char* ptr_; // pointer to the array
}; // class sorted_sc_array
#endif // A2_HPP
This is the testing class:
/*
* File: a2.pp
* Description: testing class a2.hpp
*/
#include <iostream>
#include "a2.hpp"
int main(int argc, char* argv[]) {
sorted_sc_array A;
{
sorted_sc_array T;
for (signed char c = -128; c < 127; ++c) T.insert(c);
T = T;
sorted_sc_array V = T;
A = V;
}
const auto first = A.data();
const auto last = first + A.size();
auto size = A.size();
bool res = std::is_sorted(first, last);
if (!res || (A.size() != 255)) std::cout << "fail";
else std::cout << "pass";
std::cout << std::endl;
return 0;
} // main
The code compiles and executes, with a "pass" however there is a memory leak somewhere ! :(

Answer 1

There are multiple bugs in the shown code.
In the copy constructor:
delete[] str;
This deletes the other object's buffer. The other object's destructor will attempt to delete[] its own buffer again, when it gets destroyed. This will result in memory corruption, and undefined behavior.
The obvious memory leak is in your insert():
ptr_ = (signed char*)malloc((size_)*sizeof(char));
There are two simultaneous bugs here.
Using malloc for a buffer that the destructor will eventually delete[]. Only new-ed objects can be delete[]d. Using delete for a malloc-ed content is undefined behavior.
The previous contents of ptr_ are not explicitly deleted, thus leaking memory.
The insert(), overall, is doing unnecessary allocation. There's no need to allocate a buffer twice, there. Only one allocation is sufficient: allocate, copy over the content to the new buffer, delete the old ptr_, and set ptr_ to the newly-allocated buffer.