C->C++ Automatically cast void pointer into Type pointer in C++ in #define in case of type is not given (C-style) [MSVS]

Question

Hi!

I\'ve used the following C macro, But in C++ it can\'t automatically cast void* to type*

Answer 1

To makes James' answer even dirtier, if you don't have decltype support you can also do this:

template 
class auto_cast_wrapper
{
public:
    template 
    friend auto_cast_wrapper auto_cast(const R& x);

    template 
    operator U()
    {
        return static_cast(mX);
    }

private:
    auto_cast_wrapper(const T& x) :
    mX(x)
    {}

    auto_cast_wrapper(const auto_cast_wrapper& other) :
    mX(other.mX)
    {}

    // non-assignable
    auto_cast_wrapper& operator=(const auto_cast_wrapper&);

    const T& mX;
};

template 
auto_cast_wrapper auto_cast(const R& x)
{
    return auto_cast_wrapper(x);
}

Then:

#define MALLOC_SAFE(var, size)                      \
{                                                   \
    var = auto_cast(malloc(size));                  \
    if (!var) goto error;                           \
}

I expanded on this utility (in C++11) on my blog. Don't use it for anything but evil.