Question

Following code is in simplest form:

struct X {
  operator char () const { return 'a'; }
};

int main ()
{
  X obj, *p = &obj;
  char a = *p;  // ok
  char c = (true)? *p : 'z';
}

This code gives compiler error as,

error: operands to ?: have different types ‘X’ and ‘char’

Why *p is not resolved to char when there is no ambiguity in class X for typecasting operator ?
Is such spurious error message correct or it’s a g++ bug ?

[Update Note: Interestingly this scenario doesn’t generate such error]

Answer 1

It seems to be a compiler-bug. I checked it out in the spec, the Standard clearly says (§5.16/3 – C++03),

Otherwise, if the second and third operand have different types, and either has (possibly cv-qualified) class type, an attempt is made to convert each of those operands to the type of the other.

and the rest of the section explains how the conversion is done. There is nothing that stops *p from implicitly converting into char type, using the user-defined conversion operator.

Also, I compiled it with (GCC) 4.5.0. It gives no error, with -pedantic option as well. Tried it -std=c++98 and -std=c++0x. Still no error.

Most definitely, it is a compiler-bug.