Can Matio read mat files created by version R2023a?

[Jim Houskeeper]

I am trying to read mat files created by MatLab version 2023a. If I open the files in MatLab I can see all of the variables in the file, which are a mix of structures, arrays numeric and string variables. However, when I attempt to read a variable from the file, the variable name is an empty string. As a result, if I try to read the variable using its name, Mat_VarRead returns NULL.

This is the code I am using:

matvar_t *MatLabUtilities::GetVariableFromMatFileMatio(const std::string& fileName, const std::string& variableName)
{
    matvar_t *matvar = nullptr;

    // Open MAT-file
    mat_t *matfp = Mat_Open(fileName.c_str(), MAT_ACC_RDONLY);
    if (matfp == NULL) {
        std::cerr << "Error opening MAT file" << std::endl;
        return nullptr;
    }

    // Read data from MAT-file
    matvar = Mat_VarRead(matfp, variableName.c_str());
    if (matvar == NULL) {
        std::cerr << "Error reading variable from file" << std::endl;
        Mat_Close(matfp);
        return nullptr;
    }
    return matvar;
}

Any suggestions would be greatly appreciated!

[tbeu]

• Yes, MATLAB R2023a is supported.
• Code snippet LGTM.

Can you attach the MAT file here for reproduction on my side?

[Jim Houskeeper]

Sure, here is the mat file. Really appreciate the help.

Jim

[Jim Houskeeper]

I also added some print statements to the mat.c file to try to get a better understanding of what is happening, and this is what I get:

File = mat.c, Line = 2759, mat->version = 0x100
File = mat.c, Line = 2718, class type = 17, matvar->name = (null), name = stereoParams
File = mat.c, Line = 2718, class type = 17, matvar->name = (null), name = stereoParams
File = mat.c, Line = 2718, class type = 9, matvar->name = , name = stereoParams
File = mat.c, Line = 2777, Mat_VarReadInfo failed, returning NULL

[tbeu]

This is known issue in matio about the opaque data type, see e.g. https://github.com/tbeu/matio/issues/77 .

How did you create the file in MATLAB? Can you use struct as workaround?