Question

I’m trying to write/read a double matrix to file as binary data but I’m not getting the correct values when reading.

I’m not sure if this is the correct procedure to do it with matrices.

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Here’s the code that I’m using to write it:

void writeMatrixToFileBin(double **myMatrix, int rows, int colums){
        cout << "\nWritting matrix A to file as bin..\n";

        FILE * pFile;
        pFile = fopen ( matrixOutputName.c_str() , "wb" );
        fwrite (myMatrix , sizeof(double) , colums*rows , pFile );
        fclose (pFile);
    }

Here’s the code that I’m using to read it:

double** loadMatrixBin(){
    double **A; //Our matrix

    cout << "\nLoading matrix A from file as bin..\n";

    //Initialize matrix array (too big to put on stack)
    A = new double*[nRows];
    for(int i=0; i<nRows; i++){
        A[i] = new double[nColumns];
    }

    FILE * pFile;

    pFile = fopen ( matrixFile.c_str() , "rb" );
    if (pFile==NULL){
        cout << "Error opening file for read matrix (BIN)";
    }

    // copy the file into the buffer:
    fread (A,sizeof(double),nRows*nColumns,pFile);

    // terminate
    fclose (pFile);

    return A;
}

Answer 1

It doesn’t work because myMatrix is not a single continuous memory area, it’s an array of pointers. You have to write (and load) in a loop:

void writeMatrixToFileBin(double **myMatrix, int rows, int colums){
    cout << "\nWritting matrix A to file as bin..\n";

    FILE * pFile;
    pFile = fopen ( matrixOutputName.c_str() , "wb" );

    for (int i = 0; i < rows; i++)
        fwrite (myMatrix[i] , sizeof(double) , colums , pFile );

    fclose (pFile);
}

Similar when reading.