c++ member initializer with const getter in a class

Question

Hi I get the runtime error with memory acccess violation when trying to run the following:

class MyMutable{
private :
    std::string m_name;
    mutable int m_DebugCount;
public:
    MyMutable()
        : m_name(" "), m_DebugCount(0) {}

    MyMutable(std::string& newName)
        : m_name(newName), m_DebugCount(0) {}

    std::string getName() const
    {
        ++m_DebugCount;
        return m_name;
    }
};

int main()
{
    const MyMutable k((std::string&)("Hello"));
    std::cout << k.getName() << std::endl;
}

and the error I get is beloow I get it on the seconde constructor after m_debugcount:

Exception thrown at 0x7C1436C0 (vcruntime140d.dll) in ConsoleApplication1.exe: 0xC0000005: Access violation reading location 0x011FDFA0. occurred

Answer 1

You should avoid c-style casts and use static_cast instead as it is safer. Changing your code to use static_cast:

const MyMutable k(static_cast<std::string&>("Hello"));

Results in the error:

error: non-const lvalue reference to type 'std::string' (aka 'basic_string<char>') cannot bind to a value of unrelated type 'const char [6]'
    const MyMutable k(static_cast<std::string&>("Hello"));

The solution is to change your constructor to take a const reference then you don't need to cast at all as the string literal is automatically converted to std::string:

#include <string>
#include <iostream>

class MyMutable{
private :
    std::string m_name;
    mutable int m_DebugCount;
public:
    MyMutable()
        : m_name(" "), m_DebugCount(0) {}

    MyMutable(const std::string& newName)
        : m_name(newName), m_DebugCount(0) {}

    std::string getName() const
    {
        ++m_DebugCount;
        return m_name;
    }
};

int main()
{
    const MyMutable k("Hello");
    std::cout << k.getName() << std::endl;
}