c++ - 意外的模板扣除

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 = "");

以下代码将在运行时编译并崩溃:

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

我实际上希望它根本无法编译，因为没有函数将其参数作为参数! (请注意，“MyClass，未签名”是不必要的，但只是为了清楚...)

Answer 1

遗憾的是，std::string 可以从nullptr 构造，参见here ，特别是 (5):

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

注意:

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.