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c++type-conversiondefault-parameters

default argument mismatch in C++?

Consider the following code:

#include <iostream>

class Bar
{
public:
    void foo(bool b = false, std::string name = "");
};

void Bar::foo(bool b, std::string name)
{
    if (!b)
    {
       std::cout << "b is false" << std::endl;
    }
    else
    {
       std::cout << "b is true" << std::endl;
    }
}

int main()
{
    Bar myBar;
    myBar.foo("bla");
    return 0;
}

I guess C++ is not broken, but can anyone please explain why the output is true? I am working on VS 2010 but I also checked in ideone which runs gcc

Solution

  • The compiler is implicitly casting the first parameter, a char const[4], to bool, and results in true.

    It's equivalent to

    myBar.foo((bool)"bla");

    which is also equivalent to

    myBar.foo((bool)"bla", "");