Opengl previous object disappears - opengl

Question

When I make 2 or more instance of TestLine class and add it in the render class, only the last one is rendered. The previous objects doesn't render or disappear
TestLine class:
void update(){
glEnableClientState(GL_VERTEX_ARRAY);
glBindBuffer(GL_VERTEX_ARRAY, xbo);
glVertexPointer(2, GL_FLOAT, 0, 0);
glDrawArrays(GL_LINES, 0, verts.size());
glDisableClientState(GL_VERTEX_ARRAY);
}
void set(float x, float y, float x2, float y2){
verts.push_back(x);
verts.push_back(y);
verts.push_back(x2);
verts.push_back(y2);
glGenBuffers(1, &xbo);
glBindBuffer(GL_ARRAY_BUFFER, xbo);
glBufferData(GL_ARRAY_BUFFER, verts.size() * sizeof(GLfloat), &verts[0], GL_STATIC_DRAW);
}
functions in render class
void draw(){
int size = lines.size();
for(int i = 0; i < size; i++)
lines[i]->update();
}
void add(TestLine* d){
lines.push_back(d);
}

Answer 1

glBindBuffer(GL_VERTEX_ARRAY, xbo);
GL_VERTEX_ARRAY is not a valid argument for glBindBuffer():
target: Specifies the target to which the buffer object is bound. The symbolic constant must be GL_ARRAY_BUFFER, GL_ELEMENT_ARRAY_BUFFER, GL_PIXEL_PACK_BUFFER, or GL_PIXEL_UNPACK_BUFFER.
Use GL_ARRAY_BUFFER like in your other invocation.
glDrawArrays(GL_LINES, 0, verts.size());
set() only specifies two vertices, not four. If verts contained some sort of multi-float struct (e.g.: struct Vertex { float x, y; };) instead of raw floats this would have worked.
Try this:
glDrawArrays(GL_LINES, 0, verts.size() / 2);