openGL/glut & glm ModelView Matrix

I've been trying to use modelview matrix for one of my projects but for now I get a bit unexpected results, which blocks my further progress.

GameEntity::GameEntity{
   view_matrix = glm::lookAt(glm::vec3(0.f, 0.f, 0.f), glm::vec3(0.f, 0.f, 1.f), glm::vec3(0.f, -1.f, 0.f));
   //view_matrix = glm::mat4(1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0); //glLoadIdentity 
   //returns this matrix, since model_matrix is identity then this is clean view_matrix?
   model_matrix = glm::mat4(1.0f);
}

void GameEntity::Scale(glm::vec3 vector)
{
    model_matrix = glm::scale(model_matrix, vector);
}

void GameEntity::getMatrix(GLfloat arr[16])
{
    glm::mat4 modelview = view_matrix * model_matrix;
    for (int i = 0; i < 4; i++){
        arr[i] = modelview[i][0];
        arr[i+1] = modelview[i][1];
        arr[i+2] = modelview[i][2];
        arr[i+3] = modelview[i][3];
        }
}

and now the expected result is matrix (this is what I get from glLoadIdentity and glScale(0.3,0.3,1.0))

[ 0.3, 0.0, 0.0, 0.0 ]
[ 0.0, 0.0, 0.0, 0.0 ]
[ 0.0, 0.0, 0.0, 0.3 ]
[ 0.0, 0.0, 0.3, 0.0 ]

but instead after scaling I get matrix (right one is while using directly inputed view_matrix, GameEntity commented code)

[ 0.3, 0.0, 0.0, 0.0 ]    [ 0.3, 0.0, 0.0, 0.0 ]
[ 0.0, 0.0, 0.0, 0.0 ]    [ 0.0, 0.0, 0.0, 0.0 ]
[ 0.0, 0.0, 0.0, 0.0 ]    [ 0.0, 0.0, 0.0, 1.0 ]
[ 0.0, 0.0, 0.0, 1.0 ]    [ 0.0, 0.0, 1.0, 0.0 ]

With the 1st matrix I get a circle flattened to double line, with 2nd its stretched out on single axis. Any ideas what I'm doing wrong?

Solution

Your Get Matrix function is wrong. When you iterate through the loop, you're not skipping over the right amount of elements in arr, the first iteration is

    arr[0] = modelview[0][0];
    arr[1] = modelview[0][1];
    arr[2] = modelview[0][2];
    arr[3] = modelview[0][3];

and the second goes

    arr[1] = modelview[1][0];
    arr[2] = modelview[1][1];
    arr[3] = modelview[1][2];
    arr[4] = modelview[1][3];

and so on. You have to fix that by using

for (int i = 0; i < 4; i++) {
    arr[4*i  ] = modelview[i][0];
    arr[4*i+1] = modelview[i][1];
    arr[4*i+2] = modelview[i][2];
    arr[4*i+3] = modelview[i][3];
}

BTW: Why are you bothering with a reference in your getMatrix prototype? Obviously you want to work with plain C arrays here, so just use pointers (or sized array function parameter types, which act like a pointer). void GameEntity::getMatrix(GLfloat arr[16]) works just as well and is much, much easier to read. And there's absolutely no benefit in using a pointer there.