CODEWITHSUNDEEP
g++
Garima Singh
Garima Singh

Reputation: 1490

gcc: Difference between -L and -l option AND how to provide complete path to a library

I am new to makefile stuff; so, please accept my apology if my questions are trivials.

Question 1: What is the difference between -L and -l option.

Question 2: How do you provide complete path to some library? For instance, "libeng" and "libmx", mentioned in following makefile,are located at {MATLABROOT}/bin/glnxa64

# root directory of MATLAB installation
MATLABROOT="/usr/local/MATLAB/R2011b"

all: engdemo

engdemo:
    g++ ${MATLABROOT}/extern/examples/eng_mat/engdemo.cpp -o engdemo \
        -I${MATLABROOT}/extern/include \
        -L${MATLABROOT}/extern/lib -llibeng -llibmx

clean:
    rm -f engdemo *.o

Update: Following makefile works:

# root directory of MATLAB installation
MATLABROOT="/usr/local/MATLAB/R2011b"

all: engdemo

engdemo:
    g++ ${MATLABROOT}/extern/examples/eng_mat/engdemo.cpp -o engdemo \
        -I${MATLABROOT}/extern/include \
        #-L${MATLABROOT}/extern/lib -llibeng -llibmx
    -L${MATLABROOT}/bin/glnxa64 -llibeng \
    -L${MATLABROOT}/bin/glnxa64 -llibmx

clean:
rm -f engdemo *.o

I found following link about linking libraries very useful: http://www.cs.swarthmore.edu/~newhall/unixhelp/howto_C_libraries.html

Upvotes: 33

Views: 34585

Answers (1)

ztik
ztik

Reputation: 3612

Your question is refering to gcc linker (or simply ld). Description can be found in in gcc's Options for Linking or ld's Command Line Options.

From the documentation you get

-larchive: Add archive file archive to the list of files to link. ld will search its path-list for occurrences of libarchive.a for every archive specified.

-Lsearchdir: Add path searchdir to the list of paths that ld will search for archive libraries and ld control scripts.

In your example you need to use -L to define the path where libeng and libmx libraries are located. Then use -l option to instruct ld to use these libraries.

Note that in the documentation is noted that:

ld will search its path-list for occurrences of libarchive.a for every archive specified.

Upvotes: 26

Related Questions