Question

I have a directory maths which is a library that is comprised solely of header files.
I am trying to compile my program by running the following command in my home directory:

g++ -I ../maths prog1.cpp prog2.cpp test.cpp -o et -lboost_date_time -lgsl -lgslcblas

but I get the following compilation error:

prog1.cpp:4:23: fatal error: maths/Dense: No such file or directory
compilation terminated.
prog2.cpp:6:23: fatal error: maths/Dense: No such file or directory
compilation terminated.

maths is located in the same directory(i.e. my home directory) as the .cpp files and I am running the compilation line from my home as well.

prog1.cpp and prog2.cpp have the following headers
#include<maths/Dense> on lines 4 and 6 respectively, hence I am getting the error.

how do I fix it.

Answer 1

maths is located in the same directory(i.e. my home directory) as the .cpp files

Your include path is given as -I ../maths. You need -I ./maths – or simpler, -I maths since maths is a subdirectory of the current directory, not of the parent directory. Right?

Then in your C++ file, use #include <Dense>. If you want to use #include <maths/Dense> you need to adapt the include path. However, using -I. may lead to massive problems¹, I strongly advise against this.

Instead, it’s common practice to have an include subdirectory that is included. So your folder structure should preferably look as follows:

./
+ include/
| + maths/
|   + Dense
|
+ your_file.cpp

Then use -I include, and in your C++ file, #include <maths/Dense>.

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¹⁾ Consider what happens if you’ve got a file ./map.cpp from which you generate an executable called ./map. As soon as you use #include <map> anywhere in your code, this will try to include ./map instead of the map standard header.