In computer programming, a subroutine (a.k.a. function) will often inform calling code about the result of its computation, by returning a value to that calling code.The data type of that value is called the function's return type.
In the C++ programming language, a function must be declared.The C++ function's return type is specified as a part of declaring that function.A trailing return type, a syntax feature available since C++11, is like a traditional return type, except that it is specified in a different location.
An ordinary return type is specified before the function's name.In this example of traditional C++ code, the return type of HasMultipleItems is bool:
bool CClass::HasMultipleItems A trailing return type is specified after the parameter list, following -> symbols:
auto CClass::HasMultipleItems -> bool
In modern C++, the meaning of the auto keyword will depend on its context:
auto x = 11;), the auto keyword indicates type inference. The data type for that x will be deduced from its initialization. The return type of a function can also be inferred by using auto without specifying a trailing return type (e.g.)
HasMultipleItems example on the previous section. That example only uses the auto keyword as a syntactic element, because a trailing return type is being used.Consider the task of programming a generic version of int Add(const int& lhs, const int& rhs) { return lhs + rhs; }.A proper expression of this function's return type would use the two formal parameter names with decltype: decltype(lhs + rhs).But, where a return type is traditionally specified, those two formal parameters are not yet in scope.Consequently, this code will not compile: