Thread: Looking for a solution to a memory leak with pointers in a class

Although the data is deleted, MSVC shows that the following code has a memory leak issue. Does anyone know how to fix the memory leak bug in the class? Thanks.

Code:

 

#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
#include <iostream>
class Test
{
public:
    Test(int nRows, int nCols, const double* inputData)
    {
        row = nRows;
        col = nCols;
        num = row * col;
        data = new double[num];
        for (int i = 0; i < num; i++)
            data[i] = inputData[i];
    }
    ~Test()
    {
        delete[] data;
        std::cout << "Memory released!" << std::endl;
    }
private:
    double* data;
    int row, col, num;
};
int main()
{
    double inputData[12] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 };
    Test test1(3, 4, inputData);
    _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_DEBUG);
    _CrtDumpMemoryLeaks();
    return 0;
}

It's pretty clear that your program is not leaking memory!
However, at the point that you call those debug functions, the object's destructor has yet to be called, so the memory is still allocated.
Try this version:

Code:

#define _CRTDBG_MAP_ALLOC
#include <iostream>
#include <crtdbg.h>
 
class Test
{
    int row, col;
    double* data;
public:
    Test(int nRows, int nCols, const double* inputData)
        : row(nRows), col(nCols), data(new double[row * col])
    {
        for (int i = 0; i < row * col; i++)
            data[i] = inputData[i];
    }
    ~Test()
    {
        delete[] data;
    }
    int rows() const { return row; }
    int cols() const { return col; }
};
 
void f(const double *data) {
    Test t(3, 4, data);
    std::cout << t.rows() << ',' << t.cols() << '\n';
} // t is destructed (and its memory freed) just before f() returns
 
int main()
{
    double data[12] = {
         1.0,  2.0,  3.0,  4.0,
         5.0,  6.0,  7.0,  8.0,
         9.0, 10.0, 11.0, 12.0
    };
    f(data);    
    _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_DEBUG);
    _CrtDumpMemoryLeaks();
    return 0;
}

Alternatively, you might try not calling those functions and instead adding this as the first call in main:

Code:

_CrtSetDebugFlag(_CRTDBG_LEAK_CHECK_DF);

That might not give you the false positive in your original code.

Also look here:
Find memory leaks with the CRT Library - Visual Studio (Windows) | Microsoft Learn

Note that I added a little to my original post.

You can get the same effect as john.c's post with just a pair of braces.

Code:

int main()
{
    double inputData[12] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0 };
    {
        Test test1(3, 4, inputData);
    } // now Test dtor is called here
    _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_DEBUG);
    _CrtDumpMemoryLeaks();
    return 0;
}