Question

1. First I built the Boost libraries that require building by going to /usr/local/boost_1_49_0/ and running the bootstrap.sh. This went off alright.
2. Step (1) created all the .so and .a files in /usr/local/boost_1_49_0/stage/lib
3. I tested linking against a library, say lboost_regex and #include <boost/regex> in my source code. This also went off alright.

4. Finally trying out the example on asio, I tried:

   g++ -I/usr/local/boost_1_49_0 MAIN.cpp -o MAIN -L/usr/local/boost_1_49_0/stage/lib -lboost_thread -lboost_system -lpthread
   

(4) compiled alright. But when I run the program with ./MAIN, I get the following error:

./MAIN: error while loading shared libraries: libboost_system.so.1.49.0: cannot open shared object file: No such file or directory 

Answer 1

The -L option only sets a compile-time library search path; if you want a shared library to be found at runtime then its directory must be known at runtime.

One way to set this with g++ is to pass -rpath to the linker, via the compiler; in your case you could say -Wl,-rpath -Wl,/usr/local/boost_1_49_0/stage/lib. (This embeds the directory in the executable.)

Another way is to install the libraries in a place that the linker searches by default (e.g. /usr/local/lib might be such a place, depending on how the system is configured).

Yet another way is to set an environment variable such as LD_LIBRARY_PATH (Linux or Solaris) or DYLD_LIBRARY_PATH (Mac OS X), to tell the linker where to search when launching executables from the shell where the variable is set.