Alexander,

What header file should I have to include? I tried #include but g++ compile shows the following error.

.... boost/foreach.hpp: No such file or directory

In the source code file, it doesn't only include foreach.hpp but also many other boost headers. Why only this one is showing an error? Do I need to choose another header or something?

It sounds like you have an older version of Boost installed on your system. BOOST_FOREACH was not added until version 1.34. Perhaps you have 1.33? The easy way to check the Boost version is to open up boost/version.hpp and look for the BOOST_LIB_VERSION define. Hope This Helps, Justin