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Reading data from Matlab files in C

I'm trying to learn how to use the C API to read Matlab .mat files, but it does not work as I expected:

I would just like to open a very simple .mat file called test.mat , read the value from the file and save it in the C variable. I created test.mat in Matlab using the following commands:

 > value = 3; > save ("test.mat", "value")

Below is my C code that doesn't even compile - the compiler does not seem to find the header files. See below code for compiler output. What am I doing wrong here?

The code:

 #include <stdlib.h> #include <stdio.h> #include <mat.h> #include <matrix.h> int main(int argc, char *argv[]) { double value; MATFile *datafile; datafile = matOpen("test.mat", "r"); mxArray *mxValue; mxValue = matGetVariable(datafile, "value"); matClose(datafile); value = *mxGetPr(mxArray); mxFree(mxArray); printf("The value fetched from the .mat file was: %f", value); return 0; }

Compiler Output:

 $ make animate_shot cc -I/usr/local/MATLAB/R2011a/extern/include/ animate_shot.c -o animate_shot /tmp/cczrh1vT.o: In function `main': animate_shot.c:(.text+0x1a): undefined reference to `matOpen' animate_shot.c:(.text+0x2f): undefined reference to `matGetVariable' animate_shot.c:(.text+0x3f): undefined reference to `matClose' animate_shot.c:(.text+0x4b): undefined reference to `mxGetPr' animate_shot.c:(.text+0x5e): undefined reference to `mxFree' collect2: ld returned 1 exit status make: *** [animate_shot] Error 1

(the -I flag is on the line CPPFLAGS=-I/usr/local/MATLAB/R2011a/extern/include/ in my makefile and I checked that the directory exists and contains the mat.h and matrix.h header files).

UPDATE:
I found that the libraries I need to link are libmat.so and libmx.so (as per this MathWorks help article ), being in /usr/local/MATLAB/R2011a/bin/glnxa64/ on my system. So I updated my makefile:

 CPPFLAGS =-I/usr/local/MATLAB/R2011a/extern/include/ LDFLAGS = -L/usr/local/MATLAB/R2011a/bin/glnxa64 -l mat -l mx

Now running make gives the following command:

 cc -I/usr/local/MATLAB/R2011a/extern/include/ -L/usr/local/MATLAB/R2011a/bin/glnxa64 -l mat -l mx animate_shot.c -o animate_shot

However, I still get the same errors. Any ideas?

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1 answer

This is a linker failure, not a compiler failure (and it is not related to the -I option of the compiler). You need to specify the directory where the matlab .so files are located using the -L flag and add the -l<matlab-lib-name> parameter to the end of the compiler command, which indicates the name of the matlab library.

For example:

cc -I / usr / local / MATLAB / R2011a / extern / include / -L / usr / local / MATLAB / R2011a / lib animate_shot.c -o animate_shot -lmatlab

(I do not know the exact directory in which .so are located or the name of the matlab library)

Based on a comment containing additional information:

cc -I / usr / local / MATLAB / R2011a / extern / include / -L / usr / local / MATLAB / R2011a / bin / glnxa64 animate_shot.c -o animate_shot -lmat -lmx

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