Mex compilation with header files

Hi,

I'm running Matlab on Ubuntu 12.04. I have written a C++ function simulation.cpp using the mex format. I've defined some of my functions in a separate header file that is located in the same directory as simulation.cpp. I read on the web that to compile a .cpp file with header files, I need to use -l and provide the path of the header files. When I run the following:

mex -l"/media/.../folder_containing_header_files" simulation.cpp

I get the following error

/usr/bin/ld: cannot find -l/media/.../folder_containing_header_files/
collect2: ld returned 1 exit status

mex: link of ' "simulation.mexglx"' failed.

Incidentally, all my header files are located in the same directory as simulation.cpp, which is also my working directory in matlab.

Does anybody know what the problem is?

Thanks!

Answer 1

You used the "-l" (lower-case L) option; you need to use "-I" (upper-case I). "I" for "include".

Also you might need to use a space between the option and its value.

Thanks again Walter. Yes, -I (I for include) was the problem. However, now it cannot find mex.h. Where is it located and how do I specify its location to matlab?

>> mex -I "./" simulation.cpp

Warning: You are using gcc version "4.6.3-1ubuntu5)".  The version
         currently supported with MEX is "4.4.6".
         For a list of currently supported compilers see: 
         http://www.mathworks.com/support/compilers/current_release/

simulation.cpp:2:17: fatal error: mex.h: No such file or directory
compilation terminated.

      mex: compile of ' "simulation.cpp"' failed.

Error using mex (line 206)
Unable to complete successfully.

Answer 2

If your current directly is the directory that contains simulation.cpp and its associated header files, doesn't simply "mex simulation.cpp" work at the command line?

Possibly yes.

#include "HeaderFile.hpp"

would look in the current directory, but

#include <HeaderFile.hpp>

would not look in the current directory, in which case the -I option would be needed.

Thanks James and Walter. I tried both `<HeaderFile.hpp> and "HeaderFile.hpp". It didn't help.

Are you still using -l (lower-case L)? I'm sure it should be -I (upper-case I)

Answer 3

Have you tried the function form of mex yet? I.e., something like

mex('-I','...whatever...','simulation.cpp')

Also, what do your include lines in the actual source code look like?

Same error.

>> mex('-I','./','simulation.cpp')

Warning: You are using gcc version "4.6.3-1ubuntu5)".  The version
         currently supported with MEX is "4.4.6".
         For a list of currently supported compilers see: 
         http://www.mathworks.com/support/compilers/current_release/

simulation.cpp:2:17: fatal error: mex.h: No such file or directory
compilation terminated.

      mex: compile of ' "simulation.cpp"' failed.

Error using mex (line 206)
Unable to complete successfully.

Here are my actual include lines:

#include <math.h>
#include "mex.h"
#include <iostream>
#include <iomanip> //for setw
#include <map>
#include <string>
#include <sstream> //for string stream
#include "example4channel.h" //my header file

I tried `<mex.h> (instead of "mex.h") as well, didn't help.

What happens if you try to compile this file:

// gateway.c
#include "mex.h"
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
}

with just this command:

mex gateway.c

Surprising. It works.

>> mex gateway.c

Warning: You are using gcc version "4.6.3-1ubuntu5)".  The version
         currently supported with MEX is "4.4.6".
         For a list of currently supported compilers see: 
         http://www.mathworks.com/support/compilers/current_release/

I also tried a sample cpp file using mex code that I found online, and it worked. The only difference being, the user hadn't created his own header files. So the problem occurs because I have created my own header files. I haven't found an example containing header files so far - that would help me figure out what is wrong with my code.

I would suggest adding a header file (e.g., an empty one) to the gateway.c example above and try that. Then successively build things up until you discover the problem.

The problem occurs even before I add the header file. When I do mex gateway.c, it compiles without error, but when I do mex -I "./" gateway.c, it complains of a missing mex.h file. So one guess is that it is trying to search for mex.h within my current directory. How do I tell matlab to not restrict its search to my directory, but add my directory to the list it already searches?

Frankly, I don't know for sure since I don't personally use any of these library/include/directory options myself. Things like having spaces in directory names etc tend to complicate things, so I avoid these options entirely. But I have never had a problem with the following approach:

- Have all the source and header files in one directory
- Make that directory the current directory
- Use simple #include "filename.h" syntax in source files
- Use filenames without directory info on the mex command line

Does this approach work for you?

If you were to try

mex -v gateway.c

then along the way it would probably indicate which directories it is -I'ing; you could then -I those directories for your actual code.

Answer 4

There should be no space between the switch and the directory. So can you try:

 mex -I./ gateway.c

rather than

 mex -I "./" gateway.c

Answer 5

Thank You all for your help.

James: I do have all my header files in one folder. When I tried without the -I as you suggested, I was getting an undefined reference error for all functions declared in my header file and defined in a separate cpp file (with the same name as the header file). Some web-searching revealed that I shouldn't be doing just

 mex simulation.cpp 

but instead

 mex simulation.cpp header.cpp

This worked. Sorry if this is well-known, I wasn't aware of this - I don't have a CS or compilers background.

Thanks again James, Walter and Ryan!