nonstandard extension used : 'token' : conversion from 'type' to 'type'
This type conversion is not allowed by the C++ draft standard, but it is permitted here as an extension. This warning is always followed by at least one line of explanation describing the language rule being violated.
Example
struct C { C(); }; void func(void) { //Yields: warning C4239: nonstandard extension used : //'initializing' : conversion from 'struct C' to //'struct C&' //A reference that is not to 'const' cannot be bound //to a non-lvalue C & rC = C(); }