structure does not name a type in c++

First, in C++ (but not C) every struct or class names a type. So if you declare a struct connection_header, you also get a connection_header type, so you can later declare connection_header var some variable.

Then, typedef both in C and C++ needs a type and a name. For example:

 typedef long my_number_type;

declares my_number_type as a synonym for long

So as others pointed out, drop the typedef

You are using typedef without giving a name to the type. Just drop the typedef, it is not needed here:

struct connection_header {
    string url;
    string method;
};

Next, connection_header is declared inside of the Example class, so you need to fully qualify its name in the implementation when it is a return type:

Example::connection_header Example::get_connection_header()

Try below code in cpp file, add Example:: before connection_header :

Example::connection_header Example::get_connection_header() {
    return NULL;
}

connection_header is defined inside Example so you should give it its definition scope.

Also, the keyword typedef will be ignored in C++. You can omit it