Lecture Notes by [email protected]
A library is a collection of pre-compiled object files that can be linked into your programs via the linker. Examples are the system functions such as printf() and sqrt(). There are two types of external libraries: static library and shared library.
- A static library has file extension of
.a(archive file) in Unixes or.lib(library) in Windows. - A shared library has file extension of
.so(shared objects) in Unixes or.dll(dynamic link library) in Windows. Because of the advantage of dynamic linking, g++, by default, links to the shared library if it is available. You can list the contents of a library vianm filename.
Let's suppose that you have a source file (nowic.cpp) to turn it into a static library (libnowic.a). Assume that you keep lib/nowic.cpp and ~/include/nowic.h.
g++ -c nowic.cpp -I../include // produces nowic.o
ar rcs libnowic.a nowic.o
ar // list all the options available
ar t libnowic.a // list ~.o files archived
ar x libnowic.a // extract ~.o files archived
nm nowic.o // list the actual function names in .o file
- -r: Insert the files member... into archive (with replacement).
- -c: Indicates you are creating an archive file
- -s: Write an object-file index into the archive, change is made to the archive
- -t: display contents of archive (show the list of .o files, use nm ~.o to see functions in ~.o)
It is important that you recognize that the g++ compiler requires that you prefix your static library with the keyword lib and suffix .a, like libnowic.a. The lib prefix is required by the linker to find the static library.
Assuming that you are in ~/src folder and already have ../lib/libnowic.a
g++ selection.cpp sortDriver.c -o sort –I../include –L../lib –lnowic
- -L: Indicates the location of the library you want to reference
- -l: Specifies the specific library you want to attach