Could be a memory leak on std::locale?

Question

I have a code:

std::stringstream ss;

std::locale loc(ss.getloc(), new custom_numpunct());

ss.imbue(loc);

Where custom_numpunct is defined as:

class custom_numpunct : public std::numpunct<char>
{
protected:
	virtual char do_thousands_sep() const
	{
		return ',';
	}

	virtual std::string do_grouping() const
	{
		return "\3";
	}
};

My question is: the line

std::locale loc(ss.getloc(), new custom_numpunct());

could be a memory leak? Like 7th constructor from this official page: https://en.cppreference.com/w/cpp/locale/locale/locale

std::locale l4(l1, new std::codecvt_utf8<wchar_t>);

Answer 1

These classes are derived from the locale::facet class, which implements Reference Counting (according to documentation). Therefore, in both of your examples, the objects will be deleted.

You can add a destructor to custom_numpunct to see that it is executed.

(However, some adjustments are needed to allocate the custom_numpunct or codecvt_utf8 objects on the stack).

Answer 2

There does not appear to be a memory leak. Try this using the CRT Library debugging features -

// LocLeak.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#ifdef _DEBUG
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
#ifndef DBG_NEW
#define DBG_NEW new ( _NORMAL_BLOCK , __FILE__ , __LINE__ )
#define new DBG_NEW
#endif
#endif  // _DEBUG

#include <iostream>
#include <locale>
#include <sstream>

class custom_numpunct : public std::numpunct<char>
{
protected:
    virtual char do_thousands_sep() const
    {
        return ',';
    }

    virtual std::string do_grouping() const
    {
        return "\3";
    }
};

// Only dynamically allocated int is leaked

int main()
{
    _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);

    int *pInt = ::new int;

    std::stringstream ss;

    std::locale loc(ss.getloc(), ::new custom_numpunct );

    ss.imbue(loc);

    ss << 1000000;

    std::cout << ss.str() << std::endl;

    return 0;
}