CODEWITHSUNDEEP
c++memoryvectormemory-leaksheap-memory
jazzybazz
jazzybazz

Reputation: 1887

Memory leak, vector pushback c++

I have a class Bar, its constructor initializes a std::vector of type Foo (another class).

Bar.cpp

Bar::Bar(int n) {
 for(int i = 0; i < n; i++) {
    Foo foo;
    foo.somefunction(i);
    vec.push_back(foo) //this should insert foo into the vector
  }
}

Bar.h

class Foo;
class Bar {
 std::vector<Foo> vec;
};

When I debug, the first iteration of the construction works fine. foo is created, foo.somefunction() is run fine, and foo is pushed into vec.

The second interation seems to work fine as well, but the program crashes when it goes back to start the third iteration.

I get _BLOCK_TYPE_IS_VALID(pHead->nBlockUse) error and HEAP CORRUPTION DETECTED.

Foo is a class that contains an dynamically created array, nothing special. Something like this:

Foo::Foo() {
  solution = new float[size];
  // some function that initializes the elements of solution
}

and a regular destructor ~Foo() {delete [] solution;}. I don't think the problem comes from Foo.

Upvotes: 0

Views: 2866

Answers (2)

JustAnotherCurious
JustAnotherCurious

Reputation: 2240

It looks like you didn't implement copy constructor in class Foo. In Bar constructor each iteration new instance of Foo is created and destroyed when the iteration is over. So the memory allocated in Foo is destroyed, but default copy constructor that copied instance of Foo to vector didn't copy the memory you allocate with "new", just copied the pointer. So after each iteration each vector element is corrupted. Let assume that vector had some allocated memory for your objects at the beginning. Then when there was no place in the buffer and he couldn't grow that buffer any more, vector allocates new memory and another copy operation happens. When copy operation is finished old buffer need to be freed and vector destroys all objects in old buffer and destructor in each object will call delete[] on corrupted pointer.

Upvotes: 0

Shafik Yaghmour
Shafik Yaghmour

Reputation: 158529

Most likely you did not implement the copy constructor and operator = properly and you are double deleting solution. As mentioned you should also read up on The Rule of Three.

The C++ standard containers store copies and so when you do a push_back you are making a copy.

Upvotes: 4

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