C++ “conversion loses qualifiers” compile error

Question

I ran into an interesting problem while debugging SWIG typemaps today. Anyone care to enlighten me why Visual C++ 2008 throws a \"conversion loses qualifiers\" error when co

Answer 1

In following code,

friend ostream & operator<<(ostream & output, const List& other)
{
    for(int i=0;i<other.length();i++)
        output << other.getData()[i] << " ";

    return output;
}

to remove compilation error "Conversion loses qualifiers", for parameter "const List& other", I changed both following called methods to const.

T* getData() const
{
    return data;
}

int length() const
{
    return lSize;
}

Answer 2

Say you had the following function:

void test(  const char*& pRef)
{
    static const char somedata[] = { 'a' ,'b', 'c', '\0'};
    pRef = somedata;
}

If you passed in a non-const char*, then when test() returned the compiler would have lost the fact that what p is pointing to is const.

It's essentially the same reason as given in this C++ FAQ Lite question (dealing with pointers-to-pointers rather than pointer references):

• http://www.parashift.com/c++-faq-lite/const-correctness.html#faq-18.17