Question

I am porting a quite large C/C++ project to Mac with XCode. Some C++ classes import string or vector. This causes some strange errors reporting redefinition of several std functions. For example the compiler reports redefinition of 'std::__is_integral' in <type_traits>.

I don’t get any other errors and I definitely don’t overwrite any of these std-functions. Also the error vanishes when I comment the include of string.

What might cause this behavior?

Answer 1

It turned out that somewhere in the C++ code – which I inherited for this project – there was a redefinition of bool. bool was redefined as int. Therefore in the type_traits header (and some other std-lib headers) there were duplicate method definitions of generic methods that hat a bool and an int generic parameter.

For example in type_traits there is:

template <> struct __is_integral<bool> : public true_type {};

and

template <> struct __is_integral<int> : public true_type {};

As bool was redefined as int both methods had the same signature and I got this redefinition of... error.