Linker not taking local (user) boost installation with g++ - dynamic

Question

I want to have local installation (in my home-folder (Linux), say $HOME/boost) of the boost C++ libraries in addition to a system-wide installed default of the boost libs. I built them from sorce and that worked fine.
After that, I set the environment variables CPLUS_INCLUDE_PATH and LD_LIBRARY_PATH to match the destination of the local installation, so both pointing to $HOME/boost/include and $HOME/boost/lib/, respectively.
In order to test that, I used the following code for testing the correct usage of CPLUS_INCLUDE_PATH for the headers:
#include <boost/version.hpp>
#include <iostream>
#include <iomanip>
int main()
{
std::cout << "Boost version: " << BOOST_LIB_VERSION << std::endl;
return 0;
}
Compiling it with g++ -o Test_boost_version test_boost_version.cpp works as expected, reporting the expected (local) version. Having CPLUS_INCLUDE_PATH empty gives me the boost-version of the default, system-wide installation. So far so good.
In order to test the linking, I used the following code (taken from the boost homepage:
#include <boost/regex.hpp>
#include <iostream>
#include <string>
int main()
{
std::string line;
boost::regex pat( "^Subject: (Re: |Aw: )*(.*)" );
while (std::cin)
{
std::getline(std::cin, line);
boost::smatch matches;
if (boost::regex_match(line, matches, pat))
std::cout << matches[2] << std::endl;
}
}
and built it with g++ -o Test_boost_linking test_boost_linking.cpp -lboost_regex.
Calling ldd Test_boost_linking however does NOT make use of the local installation (provided via LD_LIBRARY_PATH) but gives me: libboost_regex.so.1.42.0 => /usr/lib/libboost_regex.so.1.42.0 (0x00007f9264612000)
When I use g++ -o Test_boost_linking test_boost_linking.cpp -lboost_regex -L$HOME/boost/lib, ldd is reporting the correct library (libboost_regex.so.1.50.0 => $HOME/boost/lib/libboost_regex.so.1.50.0 (0x00007f6947d2a000)).
This is actually a problem for me since I want to set up my local environment such that a compilation will ignore the system-default boost installation and only use the local installation and I thought this is exactly what is achieved when setting the CPLUS_INCLUDE_PATH and LD_LIBRARY_PATH, but for the latter, this seems not to hold true.
So how can I make sure that using g++ -o Test_boost_linking test_boost_linking.cpp -lboost_regex (without -L) uses the local libraries?
[EDIT] Thinking of it further, I am wondering IF it is actually absolutely mandatory to use "-L$HOME/boost/lib" in the command-line (using LDFLAGS as environment variable seems to have no effect, probably just in combination with a Makefile) when using libraries in a non-standard directory?? Is this the case?
(BTW I think this will hold true also for other libraries, not only boost...)
(I used: g++ (Debian 4.4.5-8) 4.4.5)
Thank you.

Answer 1

You need to use the environment variable LIBRARY_PATH to let gcc know where to find the libraries at link time. LD_LIBRARY_PATH lets the program know where to find the dynamic libraries at runtime. This answer has more details. These links from "An Introduction to GCC" may also be useful: Compilation options:Environment Variables and Shared and Static Libraries