How do I include a path to libraries in g++

Question

I am trying to include the path to extra libraries in my makefile, but I can't figure out how to get the compiler to use that path. So far I have:

g++ -g -Wall testing.cpp fileparameters.cpp main.cpp -o test

and I want to include the path to

/data[...]/lib

because testing.cpp includes files from that library. Also, I'm on a Linux machine.

EDIT: Not a path to a library. Just to header files from that library that were included. My bad.

Possible duplicate of [How to make g++ search for header files in a specific directory?](https://stackoverflow.com/questions/12654013/how-to-make-g-search-for-header-files-in-a-specific-directory) — phuclv, Mar 08 '18 at 07:09

score 248 · Accepted Answer · edited Oct 13 '20 at 19:25

248

To specify a directory to search for (binary) libraries, you just use -L:

-L/data[...]/lib

To specify the actual library name, you use -l:

-lfoo  # (links libfoo.a or libfoo.so)

To specify a directory to search for include files (different from libraries!) you use -I:

-I/data[...]/lib

So I think what you want is something like

g++ -g -Wall -I/data[...]/lib testing.cpp fileparameters.cpp main.cpp -o test

These compiler flags (amongst others) can also be found at the GNU GCC Command Options manual:

3.16 Options for Directory Search

edited Oct 13 '20 at 19:25

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answered May 26 '11 at 15:34

Ernest Friedman-Hill

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Basically someplace before it's needed; the `-I` should come before the .cpp filenames, for example. – Ernest Friedman-Hill May 26 '11 at 15:36
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Is it possible to make the compiler figuure that out, like add the library to a system variable? – Fred Mar 15 '13 at 19:10
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@Fred, yes, g++ understands [a whole bunch of environment variables](http://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html) which can be used to control the include path, library path, etc. – Ernest Friedman-Hill Mar 16 '13 at 03:09
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what's the difference between -L and -I (capital i, not lower L)? – Youda008 Jul 25 '15 at 19:52
@Youda008 did you read this answer? It explains exactly that. – Ernest Friedman-Hill Jul 25 '15 at 19:58
@ErnestFriedman-Hill i don't understand it. "To specify a directory to search" and "To specify a directory to search for include files". So what does it search in the first case? – Youda008 Jul 25 '15 at 20:02
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@Youda008 Capital ell: search path for libraries. Capital eye: search path for include files. Small ell: name of library to link. – Ernest Friedman-Hill Jul 25 '15 at 20:35
how can I do this for makefiles? – Nam Vu Oct 19 '15 at 05:01
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@ZuzooVn do what? The -L and -l flags would just go in the LDFLAGS variable. – Ernest Friedman-Hill Oct 19 '15 at 12:45
Will include files really be placed in a lib directory? – Viesturs Dec 30 '17 at 23:28
@Viesturs Is this something that people do sometimes? Yes, absolutely. – Ernest Friedman-Hill Dec 31 '17 at 04:06
The `-l:` is very important in `cygwin` because the library name is no longer following the traditional `Unix` naming convention for example `/usr/lib/libPocoFoundation.dll.a`. So it becomes, `-l:libPocoFoundation.dll.a`. Know, that it is by Unix long tradition that `-lm` means link to `libm.so` and `cygwin` is part Unix and part Windows. – daparic Feb 07 '19 at 16:43

score 7 · Answer 2 · answered Jun 29 '20 at 12:28

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In your MakeFile or CMakeLists.txt you can set CMAKE_CXX_FLAGS as below:

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -I/path/to/your/folder")

answered Jun 29 '20 at 12:28

Kartik Javali

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score 3 · Answer 3 · answered Oct 26 '21 at 13:29

Alternatively you could setup environment variables. Suppose you are using bash, then in ~/.bashrc, write

C_INCLUDE_PATH="/data/.../lib/:$C_INCLUDE_PATH" ## for C compiler
CPLUS_INCLUDE_PATH="/data/.../lib/:$CPLUS_INCLUDE_PATH" ## for Cpp compiler
export C_INCLUDE_PATH
export CPLUS_INCLUDE_PATH

and source it with source ~/.bashrc. You should be good to go.

How do I include a path to libraries in g++

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