Question

After implementing the C++ code below, I ran valgrind --leak-check=full in order to check if there was any memory leak. The result was 0 bytes were in use at exit and no leaks are possible.

However, later I discovered that I’ve forgotten to use delete[] x instead of just delete x inside the destructor.

I searched for some explanations (for instance: delete vs delete[] operators in C++), and everything I read said that using delete without [] can cause memory leak, since it calls just the destructor for the first object in the array.

I changed the code to delete[] and the valgrind output was the same (as expected). But now I’m confused: “Is there a problem with valgrind, or does delete really works fine for arrays even without the operator []?”

#include <iostream>
#include <string.h>
using namespace std;
class Foo {
  private: char *x;
  public:
    Foo(const char* px) {
       this->x = new char[strlen(px)+1];
       strcpy(this->x, px);
    }
    ~Foo() {
       delete x;
    }
    void printInfo() {  cout << "x: " << x << endl;  }
};
int main() {
   Foo *objfoo = new Foo("ABC123");
   objfoo->printInfo();
   delete objfoo;
   return 0;
}

Answer 1

using delete without [] causes memory leak.

No, it causes Undefined Behavior.

Your program where you allocate using new [] and deallocate using delete has Undefined Behavior. Actually, you are lucky(rather unlucky) it doesn’t show some weird behavior.

As a side note, You also need to follow the Rule of Three for your class. Currently, you don’t do so and are calling for trouble in near future.