MATLAB: Error LNK2019: unresolved external symbol when compiling MEX

ccompilationcpplinkageMATLABmex

I'm trying to compile some files into MEX and I get a linkage error.
I have:
  • helloworld.cpp which includes gateway function
  • ftdi.h class declaration
  • ftdi.cpp a source file
  • FTD2XX.h and FTD2XX.lib a library and a header
All files are in the same folder and this folder is my current working directory in MATLAB.
I'm using MS VS2010 and MATLAB R2013a on a 64bit Windows 7. I set up the compiler using mex -setup and was able to create and run some test MEX files.
As I understand, I need to compile both helloworld.cpp and fdti.cpp when I run
mex helloworld.cpp fdti.cpp
I get:
ftdi.obj : error LNK2019: unresolved external symbol __imp_FT_ListDevices referenced in function "public: int __cdecl ftdi::GetDeviceCount(void)" (?GetDeviceCount@ftdi@@QEAAHXZ) 
ftdi.obj : error LNK2019: unresolved external symbol __imp_FT_Open referenced in function "public: int __cdecl ftdi::OpenDevice(int)" (?OpenDevice@ftdi@@QEAAHH@Z)
and more of similar errors.
ftdi::GetDeviceCount(void)
and
ftdi::OpenDevice(int)
are functions in ftdi.cpp
I also tried:
mex helloworld.cpp
and got similar errors. When I tried:
mex -IC:\Users\tnosov\Documents\MATLAB\newtest20nov helloworld.cpp
this is the path to where all my files are located and I got the same errors.
I've been stuck with this problem for many days now, I tried many other things I found here and in other places on the internet, but nothing helps. I'll be thankful for any suggestions and comments.
Thank you!
Tim
here's helloworld.cpp:
#include <mex.h>
//for FTDI
#include "ftdi.h"
ftdi usb;  //initialize an instance of class ftdi
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[    
//     {
//         mexPrintf("bye World!\n");
//         cout << endl << "Error initializing device";
//     }
//     else
//     {])
{
      mexPrintf("Hello Worl
  //     }
 d!\n");   
}

Best Answer

So here's my solution and explanation:
The error I got:
error LNK2019: unresolved external symbol __imp_FT_ListDevices referenced in function "public: int __cdecl ftdi::GetDeviceCount(void)" (?GetDeviceCount@ftdi@@QEAAHXZ)
This means that in the function ftdi::GetDeviceCount(void) the program couldn't understand what FT_ListDevices means. The declaration and definition of FT_ListDevices was in a library called ftd2xx. What I was trying to do initially, when I was trying to compile MEX file I was trying to link my program with ftd2xx.dll. However, for MEX files you need to link them with lib library, ftd2xx.lib. So I found and downloaded lib version of the library and run this command:
mex -lFTD2XX -L"C:\Users\tnosov\Downloads\CDM 2.08.30 WHQL Certified (1)\CDM v2.08.30 WHQL Certified\amd64" control_robot.cpp ftdi.cpp
where:
-lFTD2XX
is the name of the library. Note that this is lower case "L" and there's no space between -l and name of the library. Also, MATLAB adds .lib after whatever you wrote there.
-L"C:\Users\tnosov\Downloads\CDM 2.08.30 WHQL Certified (1)\CDM v2.08.30 WHQL Certified\amd64"
is location of that library. No space after -L and put quotes around path
control_robot.cpp ftdi.cpp
are the files where my code is. In this files I also included header for that library that caused me problems:
#include "C:\Users\tnosov\Dropbox\CO-OP2013\not shared\Code\interfacing_matlab_cpp\CDM 2.08.30 WHQL Certified\CDM v2.08.30 WHQL Certified\ftd2xx.h"
The way I included this header is a pretty horrible programming practice, but it works.
I hope this helps! Let me know if you have run into any kind of similar questions. I spent 2 weeks trying to fix this. I'll be glad to help you!
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