Problem with Boost::Asio for C++

Question

Hi there,

For my bachelors thesis, I am implementing a distributed version of an algorithm for factoring large integers (finding the prime factorisation). This has applications in e.g. security of the RSA cryptosystem.

My vision is, that clients (linux or windows) will download an application and compute some numbers (these are independant, thus suited for parallelization). The numbers (not found very often), will be sent to a master server, to collect these numbers. Once enough numbers have been collected by the master server, it will do the rest of the computation, which cannot be easily parallelized.

Anyhow, to the technicalities. I was thinking to use Boost::Asio to do a socket client/server implementation, for the clients communication with the master server. Since I want to compile for both linux and windows, I thought windows would be as good a place to start as any. So I downloaded the Boost library and compiled it, as it said on the Boost Getting Started page:

bootstrap

.\bjam

It all compiled just fine. Then I try to compile one of the tutorial examples, client.cpp, from Asio, found (here.. edit: cant post link because of restrictions). I am using the Visual C++ compiler from Microsoft Visual Studio 2008, like this:

cl /EHsc /I D:\Downloads\boost_1_42_0 client.cpp

But I get this error:

/out:client.exe

client.obj

LINK : fatal error LNK1104: cannot open file 'libboost_system-vc90-mt-s-1_42.lib'

Anyone have any idea what could be wrong, or how I could move forward? I have been trying pretty much all week, to get a simple client/server socket program for c++ working, but with no luck. Serious frustration kicking in.

Thank you in advance.

Answer 1

The reason the build is failing is because it cannot find the library file containing boost system. Boost includes a "handy" autolinking feature, such that when you include a header file for a binary libaray (as opposed to a header only library), boost automatically tells the compiler that it should link in the library. The downside to this is that boost doesn't tell the compiler where to find the library.

The short answer is to read a little further in the boost getting started guide. This page shows you how to add the necessary flags to the compiler command line: Getting started on windows: linking from the command line.

The first thing you have to do is find the .lib file. Boost hides them in a deep directory structure, so search for it starting in the directory you ran bjam from. Make note of the directory where the file is. You may also wish to use bootstrap --prefix=/some/install/location and bjam install to install boost somewhere other than the source directory in which you built it.

Are you building your project using a Visual Studio solution, or on the command line?

If you are using a solution file, find the link page in the solution properties. There should be a box where you can enter additional library paths. Add the directory in which you boost .lib files reside to this box.

If you are using cl on the command link, familiarize yourself with the command line options for cl and link. You can pass commands to the linker using the cl option /link, and the linker command you are looking for is /libpath.