Vector subscript out of range when trying to load Obj files in DirectX 11

Question

I am getting a vector subscript out of range when I try to load Obj files that doesnt have normals or texture coordinates. If I load an obj file that has normals and texture coordinates, then everything works fine. So I am just asking how can I modify my code to load obj files without normals and texture coordinates.

this is my struct to store VERTEX data

struct VERTEX
{
    XMFLOAT3 position;
    XMFLOAT3 normal;
    XMFLOAT2 texcoord;
};

and these vertex's are used to store the data in

std::vector<XMFLOAT3> m_position;
std::vector<XMFLOAT2> m_texCoords;
std::vector<XMFLOAT3> m_normals;
std::vector<VERTEX> m_vertices;
std::vector<DWORD> m_Indices;
VERTEX vertex;

This is how I read the lines for my faces. This all works fine but I am not sure if it may be the cause to why my program breaks when loading obj files without normals and texture coordinates.

        else if (strcmp(buffer, "f") == 0)
        {
            int fPosition, fTexCoord, fNormal; //data of a single vertex

            for (int iFace = 0; iFace < 3; iFace++)
            {
                ZeroMemory(&vertex, sizeof(VERTEX));
                file >> fPosition;
                vertex.position = m_position[fPosition - 1];

                if (file.peek() == '/')
                {
                    file.ignore();

                    if (file.peek() != '/')
                    {
                        file >> fTexCoord;
                        vertex.texcoord = m_texCoords[fTexCoord - 1];
                    }

                    if (file.peek() == '/')
                    {
                        file.ignore();
                        file >> fNormal;
                        vertex.normal = m_normals[fNormal -1];
                    }

                    m_vertices.push_back(vertex);
                    m_Indices.push_back(m_vertices.size() - 1);

                }
            }
        }

and finally this is how I set up my vertex buffer

D3D11_INPUT_ELEMENT_DESC vertlayout[] =
{
    { "POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 0, D3D11_INPUT_PER_VERTEX_DATA, 0 },
    { "NORMAL", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 24, D3D11_INPUT_PER_VERTEX_DATA, 0 },
    { "TEXCOORD", 0, DXGI_FORMAT_R32G32_FLOAT, 0, 36, D3D11_INPUT_PER_VERTEX_DATA, 0 },
};

ID3D11Device* pDevice = m_shader->GetDevice();
ID3DBlob* pVSBlob = m_shader->GetVSBlob();

pDevice->CreateInputLayout(vertlayout, ARRAYSIZE(vertlayout), pVSBlob->GetBufferPointer(),
    pVSBlob->GetBufferSize(), &m_vertexLayout);

D3D11_BUFFER_DESC bd;
ZeroMemory(&bd, sizeof(bd)); 
bd.Usage = D3D11_USAGE_DEFAULT;
bd.ByteWidth = sizeof(VERTEX)* m_vertices.size();
bd.BindFlags = D3D11_BIND_VERTEX_BUFFER;
bd.CPUAccessFlags = 0;

D3D11_SUBRESOURCE_DATA initData;
ZeroMemory(&initData, sizeof(initData));
initData.pSysMem = &m_vertices[0]; //This is where it breaks                                                                  

pDevice->CreateBuffer(&bd, &initData, &m_vertexBuffer);

bd.Usage = D3D11_USAGE_DEFAULT;
bd.ByteWidth = sizeof(DWORD)* m_Indices.size();
bd.BindFlags = D3D11_BIND_INDEX_BUFFER;
bd.CPUAccessFlags = 0;
initData.pSysMem = &m_Indices[0]; //and it breaks here too

pDevice->CreateBuffer(&bd, &initData, &m_indexBuffer);

}

as the comment says, on the lines with initData.pSysMem = &m_vertices[0]; and initData.pSysMem = &m_Indices[0];, my program will break and I will get the vector subscript out of range error. if I remove the [0] from &m_vertices and &m_Indices, it wont break however nothing will get rendered.

I would just like to know what can I do to have my obj loader load obj files that doesnt need to have always all 4 vertices, normals, texture coordinates and faces.

score 2 · Answer 1 · edited Jun 20 '20 at 09:12

In general

You cannot find out why your app crashes just by guessing. And you don't need to. As programmers, we have decent tools to solve such issues. So, general advice: learn to use your debugger.

Concrete issue

Your vectors are empty.
When you are trying to access first elements (m_vertices[0] and m_Indices[0]), which do not exist, you get this assertion failure (because you are in debug mode; in release mode it will silently trigger undefined behavior).

How to check

When program execution breaks on those lines, check "Call stack" window, to see in which function you are. Find one of your functions, that are highest on the stack and click it. Check "Locals", "Auto" or "Watch" windows (menu "Debug"->"Windows") to see contents of the vectors and other variables in scope. Place breakpoints and restart app if needed.

How to fix

Set breakpoints earlier in the program, to see why your vectors are empty. Move line by line, function by function, using "Step into" and "Step over", , watch variables, untill you will find source of error.

If it is valid to have empty vectors there, you can just make branches to avoid code paths where you accessing it's contents:

if(!m_vertices.empty())
{
    // Create buffers with data
} 
else 
{
    // Create empty buffers or report an error
}`

Hope it helps.

Vector subscript out of range when trying to load Obj files in DirectX 11

1 Answers1

In general

Concrete issue

How to check

How to fix