Why do parentheses make a difference when initializing an empty vector?
c++, compiler-errors, stl
Solution
This is actually a function declaration:
TRouteMarkets::mapped_type mapped();
declaring a function named `mapped` that accepts no arguments and returns a `TRouteMarkets::mapped_type`.
Problem
I'm having trouble understanding an error. I'm working with a straightforward map of vectors (keyed by strings and storing vectors of strings): ``` typedef std::map<std::string, std::vector<std::string> > TRouteMarkets; ``` The following code (stripped down), ``` void CFoo::Bar(const char* route, const char* market) { // ... TRouteMarkets::key_type key(route); TRouteMarkets::mapped_type mapped(); TRouteMarkets::value_type pair(key, mapped); // ... } ``` produces the following error: "Foo.cc", line 518: Error: Could not find a match for std::pair<const std::string, std::vector<std::string>>::pair(const std::string, std::vector<std::string>()) needed in CFoo::Bar(const char*, const char*). But removing the `()` from mapped, i.e. ``` TRouteMarkets::mapped_type mapped; ``` fixes the error. Why? Isn't `mapped` an empty vector of strings in either case?