[SlySven]

Like what it says: the compiler cannot find the telnet.h header file in the places where it is looking for system header files i.e. not specific to the current application/project. I'm not that familiar with MinGW but I suspect you are missing either a networking or more specifically a telnet "Package" if that is the word to use for MinGW. In many systems it is often the case that to RUN an application you need certain libraries that provide specific types of functionality but to COMPILE an application that uses those libraries you need additional information i.e. header(s) files that may be bundled up in a development version of the "Package" and might be called say "Package-development" or "Package-dev". I don't have a system with MinGW to hand so I can't be more specific than this but I hope that it might give you some pointers.

P.S. The reason I say that it is a system library you are missing is because it is enclosed by '<' and '>' characters not '"' (that is a single quoted double quote BTW!) which would be the case for headers included in the project's files.

P.P.S. The only reason that it started to compile before bailing out is that this wasn't the first file that was compiled, but if you retry it is the current thing in the list of things to compile so make will stop again pretty quickly. M.B. Make will bail out at the first error unless you give it the "-k" option to "keep going" as far as possible; that will not cause everything to be done because there are still errors, but it will point out to you other "missing headers" for any other files so you can try and fix as many as possible for the next time before retrying... Of course if you are missing a "library" AS WELL as it's headers at first then, when you HAVE got the headers in place, the "linking" phase at the end will fail as it will not be able to combine all those "*.o" object files made from each source file {*.c or *.cpp} with the "libraries" {that are in the *.dll files on windows systems} to make the *.exe executable application. Typically THAT will fail with something like "ld: undefined reference to .....".