getting around the "undefined reference to getaddrinfo" issue

>> main.cpp:(.text+0x18b): undefined reference to `getaddrinfo@16'

>> collect2: ld returned 1 exit status

After spending some time looking into winsock2 and *trying* to put together some code I've come across the message above when trying to compile the app.

After some trial and error I finally found out the reason why this message wouldn't go away. Apparently there are two things that have to be taken into account here.

1. Redefine your Windows version

According to msdn(1), some functions are only available to specific windows versions and therefore one must explicitly tell the compiler that the program is being compiled for that particular version. As it turns out, this is the case of the getaddrinfo() function.

By taking a quick look at the tcp/ip specific extensions for Winsock2 header file (ws2tcpip.h) it's easy to see this OS version dependency in the function declaration:

(...)

#if (_WIN32_WINNT >= 0x0501)

void WSAAPI freeaddrinfo (struct addrinfo*);

int WSAAPI getaddrinfo (const char*,const char*,const struct addrinfo*,struct addrinfo**);

int WSAAPI getnameinfo(const struct sockaddr*,socklen_t,char*,DWORD,char*,DWORD,int);

#else

(...)

In order to tell the compiler your windows version you can set the constant called _WIN32_WINNT to the hex code of that version.

Since the getaddrinfo() is available to Windows XP onwards, it is sufficient to use that windows version code as the value of the constant mentioned above. Add the following line before the inclusion of the headers.

#define _WIN32_WINNT 0x0501

Bear in mind that since you're telling the compiler that you're using Windows XP here, you will not be able to make use of functions that are only available to versions prior to the one you have defined (Windows XP).

2. Link, Link, Link

Easy to forget, but you must remember to link the library that implements the getaddrinfo() to your application otherwise the compiler cannot resolve the function.

The library in question is the "Ws2_32.Lib" which, in my case, came along with the Windows SDK. Once you have the full path of the URL, you can link it by using the following command:

c:\apps\g++ main.cpp "c:\xxxxxxxxxx\xxx\" -o main.exe

NB: I am disregarding here any other library that you may have to link to your app.

By following the two steps above you should be able to run your app fine.

Just remember that these steps may vary depending on the version of your compiler and the libraries you've got installed.

Intro

Ok guys, first day posting actual content on this blog.
To start off, a few answers for a couple of non-asked questions:

Who am I?

I'm a web developer living in London who got tired of writing software for the web world and feel excited by the prospect of jumping into a more research-related area of computing, namely, Image processing. As such, decided to jump on C++, a decent fast and general-purpose language. I studied Computer Science for 3 years some time ago in a far away country and I have been kind of missing all that lately. Being out of touch with that for a few years, I hope that with a bit of luck and hard work I can turn my life round and follow the direction I should never steered away from.

Who is this blog targeted to?

Well, anyone who is interested in programming in general, C++ language in particular. I would say that it would probably suit beginners, those who like me are shifting from another language to C++ or anyone interested in reading a bit about programming. If you don't actually fit in one of the stereotypes above, don't worry, everyone is welcome. So feel fee to contribute by using the comments section!

What am I going to be posting here?

Anything related to programming, really. The aim is focus on general programming, with no language in particular, although I must say I will be emphasizing C++ at first. I also can't promise I will keep the blog free from the that odd post about something else, but will do my best to keep it focused.

Aims

I would be more than happy if I could help people like me, who are also learning C++ and have encountered problems along the way. I will try to help solving basic problems that affect most people who are still beginning in C++ and perhaps the more intermediate ones.

I hope this blog helps the folks out there who are working hard to become good C++ programmers one day. As the old cliche goes, every journey of 1000 miles starts with the first step. Here is my first one.

That's all for today folks.

Roger

Newborn

At last, my blog has come out of the oven.