CODEWITHSUNDEEP
clinuxgcclinkershared-libraries
Ulrik
Ulrik

Reputation: 1141

Linking shared libraries with gcc on Linux

I need to compile and, most importantly, link a C program that uses a proprietary function present in a shared library file. Because of lack of communication with the previous development team, there is no proper documentation. I declared a function prototype (because I know the number and type of arguments):

int CustomFunction(unsigned char *in, int size);

Since that function name can be grepped from /customlibs/libcustom.so, I tried to compile the code and link it like this:

gcc -L/customlibs testing.c -o testing -lcustom

Which throws a few error messages looking like this:

/customlibs/libcustom.so: undefined reference to `AnotherCustomFunction'

Obviously, I need to tell linker to include other libraries as well, and, to make things worse, they need to be in certain order. I tried exporting LD_LIBRARY_PATH, using -Wl,-rpath=, -Wl,--no-undefined and -Wl,--start-group. Is there an easy way to give the linker all the .so files without the proper order?

Upvotes: 0

Views: 3556

Answers (3)

Ulrik
Ulrik

Reputation: 1141

I found the solution (or a workaround) to my problem: adding -Wl,--warn-unresolved-symbols, which turns errors to warnings. Note that this works only if you are ABSOLUTELY certain your function does not depend on the symbols mentioned in undefined refernce to: messages.

Upvotes: 1

kzsnyk
kzsnyk

Reputation: 2211

You should also include all the header files of your shared library by adding the -I option of gcc, for example : gcc [...] -I/path/to/your/lib/header/files [...]

Upvotes: 0

jhagen
jhagen

Reputation: 62

Add them on the command line is a way to do it. Something like this below. The LD_LIBRARY_PATH tells gcc where to look for libraries, but you still need to say what libraries to include.

gcc -L/customlibs testing.c -o testing -lcustom -lmylib1 -lmylib2 -lmylib3

Upvotes: 0

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