How do I statically compile boost_iostreams? - c++

Question

I'm new to creating Makefiles. I can successfully compile my program when using dynamic linking, but I get "undefined reference to" errors when trying to compile statically.
CC=g++
CXXFLAGS= -g -Wall -Wextra
#LDFLAGS= -g -l boost_iostreams #this works for dynamic linking
LDFLAGS= -Wl,-Bstatic -lboost_iostreams -Wl,-Bdynamic
default: zoneParserTester
zoneParser:
$(CC) $(CXXFLAGS) $(LDFLAGS) $#.cpp
zoneParserTester: zoneParser.o
$(CC) $(CXXFLAGS) $(LDFLAGS) zoneParser.o -o $# $#.cpp
gzExample:
$(CC) $(CXXFLAGS) $(LDFLAGS) -o $# $#.cpp
After searching online it seemed that the correct arguments to use are: "-Wl,-Bstatic -lboost_iostreams -Wl,-Bdynamic". Can anyone show me what I am doing wrong?

Answer 1

You are missing an important distinction between static and dynamic linking. Dynamically linking your applications A to a library B will pull in all dependencies of library B at runtime without you needing to specify them explicitly. When statically linking your application you also need to include all dependencies of library B (and the dependencies of the dependencies, and so on) at link-time in the same order as the dependency chain (so if application A depends on library B, and library B depends on library C, you must specify the libraries in that order; this is also true for .o files).
To figure out the whole dependency chain (and it's order) of a specific library can be a bit of a hassle. Sometimes the error messages during linking can give you some hints. If that doesn't help, there are several other ways:
Make an informed guess: one way to guess what libboost_iostreams depends on is by looking at what the dynamic version of the library depends on. You can do this with the ldd tool:
$ ldd /usr/lib/libboost_iostreams.so.1.46.1
On my computer it depends on libz and libbz2. So I'm pretty sure that your application will link if you just add
-lbz2 -lz
To the line where you link your application. I'm not sure if the -Wl,-Bstatic is necessary. For me, just specifying -static is sufficient:
$ gcc -static -o test test.cpp -lboost_iostreams -lbz2 -lz
Use pkg-config: most packages (unfortunately not boost) will install pkg-config files which keeps track of exactly how you must link your program to use a specific library. For example, say you would like to statically link to libcairo:
$ pkg-config --static --libs cairo
-pthread -lcairo -lgobject-2.0 -lffi -lpixman-1 -lfontconfig -lexpat -lfreetype -lpng12 -lz -lm -lxcb-shm -lxcb-render -lXrender -lglib-2.0 -lrt -lpcre -lX11 -lpthread -lxcb -lXau -lXdmcp
Use .la files and libtool: this is a somewhat deprecated method and increasingly not used anymore so the availability of .la files will depend on your distribution. libtool is yet another tool to get around this problem. When linking, instead of using g++ directly, you use a wrapper called libtool:
$ libtool --mode=link gcc -static -o my_app -lboost_iostreams
libtool will try to add the necessary libs and pass them automatically to gcc. It does this by searching for a file with the same name as the library (in your case libboost_iostreams), but with the suffix .la (instead of .a). If you open the .la file in a text editor you will see that it lists the dependencies of libboost_iostreams. I personally don't like libtool, it's a bit tricky to setup and is increasingly not used anymore. I'd probably just look at the .la file and add the dependencies manually.