VBOs with std::vector

Question

I've written a model loader in C++ an OpenGL. I've used std::vectors to store my vertex data, but now I want to pass it to glBufferData(), however the data types are wildly different. I want to know if there's a way to convert between std::vector to the documented const GLvoid * for glBufferData().

Vertex type

typedef struct {     float x, y, z;     float nx, ny, nz;     float u, v; } Vertex;  vector<Vertex> vertices; 

glBufferData() call

glBufferData(GL_ARRAY_BUFFER, vertices.size() * 3 * sizeof(float), vertices, GL_STATIC_DRAW); 

I get the following (expected) error:

error: cannot convert ‘std::vector<Vertex>’ to ‘const GLvoid*’ in argument passing 

How can I convert the vector to a type compatible with glBufferData()?

NB. I don't care about correct memory allocation at the moment; vertices.size() * 3 * sizeof(float) will most likely segfault, but I want to solve the type error first.

Answer 1

If you have a std::vector<T> v, you may obtain a T* pointing to the start of the contiguous data (which is what OpenGL is after) with the expression &v[0].

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In your case, this means passing a Vertex* to glBufferData:

glBufferData(    GL_ARRAY_BUFFER,    vertices.size() * sizeof(Vertex),    &vertices[0],    GL_STATIC_DRAW ); 

Or like this, which is the same:

glBufferData(    GL_ARRAY_BUFFER,    vertices.size() * sizeof(Vertex),    &vertices.front(),    GL_STATIC_DRAW ); 

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You can rely on implicit conversion from Vertex* to void const* here; that should not pose a problem.