Equivalent memcpy different results? - c++

Question

I used memcpy to copy a struct Vertex comprised of glm::vec3 objects.
It worked to copy the struct in a class function.
It did not work in the copy constructor that was called when that function returned the class object.
Why?
Class function returning object
ShapeData ShapeGenerator::drawTriangle() {
ShapeData ret;
Vertex verts[] = {
glm::vec3(0.0f, 1.0f, 0.0f),
glm::vec3(1.0f, 0.0f, 0.0f),
glm::vec3(-1.0f, -1.0f, 0.0f),
glm::vec3(0.0f, 1.0f, 0.0f),
glm::vec3(1.0f, -1.0f, 0.0f),
glm::vec3(0.0f, 0.0f, 1.0f),
};
ret.numVerts = NUM_ARRAY_ELEMENTS(verts);
ret.verts = new Vertex[ret.numVerts];
memcpy(ret.verts, verts, sizeof(verts)); //WORKS
GLushort indicies[] = {0,1,2};
ret.numIndicies = NUM_ARRAY_ELEMENTS(indicies);
ret.indicies = new GLushort[ret.numIndicies];
memcpy(ret.indicies, indicies, sizeof(indicies));
return ret;
}
Copy Constructor
ShapeData(const ShapeData& data) {
verts = new Vertex[data.numVerts];
//memcpy(verts, data.verts, sizeof(data.verts)); //DOES NOT WORK
std::copy( data.verts, data.verts + data.numVerts, verts);
indicies = new GLushort[data.numIndicies];
memcpy(indicies, data.indicies, sizeof(data.indicies));
numVerts = data.numVerts;
numIndicies = data.numIndicies;
std::cout << numVerts << std::endl;
}
Vertex:
#ifndef VERTEX_H
#define VERTEX_H
#include <glm/glm.hpp>
struct Vertex {
glm::vec3 position;
glm::vec3 color;
};
#endif

Answer 1

memcpy(verts, data.verts, sizeof(data.verts)); //DOES NOT WORK
does not work since verts is a pointer, not an array. sizeof(data.verts) does not evaluate to the size of the array the pointer points to. It simply evaluates to the size of a pointer on your platform.
You should be able to use:
size_t n = sizeof(*data.verts)*data.numVerts;
memcpy(verts, data.verts, n);