Question

template< typename T >
void addVarCB(const std::string &name,
              TwSetVarCallback setCallback, TwGetVarCallback getCallback,
              void * clientData, const std::string &def = "" );

template< class C, typename T >
void addVarCB(const std::string &name,
              C * _this, T(C::*getter)(void), const std::string &def = "");

The following code will compile and crash on runtime:

bar_->addVarCB<MyClass, unsigned>("foo", this, &MyClass::MyClassFn, nullptr);

I would actually expect it NOT to compile at all, as there is no function that takes its parameters as an argument! (note that “MyClass, unsigned” is unnecessary but just to be clear…)

Answer 1

Sadly, std::string is constructible from nullptr, see here, specifically (5):

basic_string( const CharT* s, // <== 'nullptr' matches here
              const Allocator& alloc = Allocator() );

Note:

5) Constructs the string with the contents of null-terminated character string pointed to by s. The length of the string is determined by the first null character. s must not be a NULL pointer.