Debug Assertion Failed in such simple example

Question

main.cpp

#include <iostream>
#include "Simple.h"

using namespace std;

int main()
{
    Simple s;
    s = Simple();
}

Simple.cpp

#include "Simple.h"

Simple::Simple(void)
{
    ptr = new int[10];
}


Simple::~Simple(void)
{
    delete [] ptr;
}

Simple.h

#pragma once
class Simple
{
public:
    Simple(void);
    ~Simple(void);

private:
    int* ptr;
};

When I run main.cpp, program stops and return an error:

Microsoft Visual C++ Debug Library Debug Assertion Failed!

Program: ...ts\Visual Studio 2010 C++\simple error\Debug\simple error.exe File: f:\dd\vctools\crt_bld\self_x86\crt\src\dbgdel.cpp Line: 52

Expression: _BLOCK_TYPE_IS_VALID(pHead->nBlockUse)

For information on how your program can cause an assertion failure, see the Visual C++ documentation on asserts.

(Press Retry to debug the application)

Why it happens in such common example?

Take a look at the [rule of 3](http://stackoverflow.com/questions/4172722/what-is-the-rule-of-three) — πάντα ῥεῖ, Nov 10 '13 at 22:52

score 3 · Answer 1 · answered Nov 10 '13 at 22:55

You need to add a copy constructor and assignment operator. At the moment, your line

s = Simple();

does the following:

Creates a temporary Simple, allocating memory for its pointer to point to.
Assigns it to s, which simply copies the pointer across from the temporary.
Destroys the temporary again, deallocating the memory now pointed to by both the pointer in the temporary and the pointer in s.

At this point, the pointer in s points to deallocated memory. When s goes out of scope, the Simple destructor tries to deallocate the memory s's pointer points to again, and undefined behaviour occurs (in your case, your program crashes).

Thank you very much for the clarying response. – user2551229 Nov 10 '13 at 23:10 — user2551229, Nov 10 '13 at 23:10

Debug Assertion Failed in such simple example

1 Answers1