c++ : 关于函数重载

Question

假如有以下类声明

#pragma once

#include <glm\glm.hpp>
#include <GL\glew.h>

class Vertex
{
public:
    Vertex(const glm::vec3& pos)
    {
        this->pos = pos;
    }
protected:
private:
    glm::vec3 pos;
};

class Mesh
{
public:
    Mesh(Vertex* vertices);
    Mesh(Vertex* vertices, unsigned int numVertices);
    
    void Draw();
    virtual ~Mesh();

protected:
private:
    Mesh(const Mesh& other);
    void operator=(const Mesh& other);

    enum
    {
        POSITION_VB,
        NUM_BUFFERS
    };

    GLuint m_vertexArrayObject;
    GLuint m_vertexArrayBuffers[NUM_BUFFERS];
    unsigned int m_drawCount;
};

定义

#include "mesh.h"

#include "debug.h"

Mesh::Mesh(Vertex* vertices)
{
    //bug::debug d;
    debug_out(("Mesh(a) >>\n"));
    debug_out(("    sizeof(Vertex):%d\n", sizeof(Vertex)));
    debug_out(("    sizeof(glm::vec3):%d\n", sizeof(glm::vec3)));
    debug_out(("    sizeof(vertices):%d\n", sizeof(vertices)));
    debug_out(("    sizeof(vertices[0]):%d\n", sizeof(vertices[0])));
    debug_out(("    n:%d\n", sizeof(Vertex) / sizeof(vertices[0])));
    Mesh(vertices, sizeof(vertices)-1);
}

Mesh::Mesh(Vertex* vertices, unsigned int numVertices)
{

    debug_out(("Mesh(a,b) >>\n"));
    debug_out(("    numVertices:%d\n", numVertices));
    debug_out(("    sizeof(vertices[0]):%d\n", sizeof(vertices[0])));

    m_drawCount = numVertices;

    //VAO
    glGenVertexArrays(1, &m_vertexArrayObject);
    glBindVertexArray(m_vertexArrayObject);

    glGenBuffers(NUM_BUFFERS, m_vertexArrayBuffers);
    glBindBuffer(GL_ARRAY_BUFFER, m_vertexArrayBuffers[POSITION_VB]);
    glBufferData(GL_ARRAY_BUFFER, numVertices * sizeof(vertices[0]), vertices, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

    glBindVertexArray(0);
}

Mesh::~Mesh()
{
    glDeleteVertexArrays(1, &m_vertexArrayObject);
}

void Mesh::Draw()
{
    glBindVertexArray(m_vertexArrayObject);
    glDrawArrays(GL_TRIANGLES, 0, m_drawCount);

    glBindVertexArray(0);
}

调用

// 设置三角形顶点
    Vertex vertices[] = { 
        Vertex(glm::vec3(-0.5, -0.5, 0)), 
        Vertex(glm::vec3(0, 0.5, 0)), 
        Vertex(glm::vec3(0.5, -0.5, 0)), 
    };
    //bug::debug d;
    debug_out(("main >>\n"));
    debug_out(("    sizeof(Vertex):%d\n", sizeof(Vertex)));
    debug_out(("    sizeof(glm::vec3):%d\n", sizeof(glm::vec3)));
    debug_out(("    sizeof(vertices):%d\n", sizeof(vertices)));
    debug_out(("    sizeof(vertices[0]):%d\n", sizeof(vertices[0])));
    debug_out(("    n:%d\n", sizeof(vertices) / sizeof(vertices[0])));

    Mesh mesh(vertices, sizeof(vertices) / sizeof(vertices[0]));
    //Mesh mesh(vertices);

问题,在调用的时候，按2个参数实例化Mesh类，能出来正确结果，

Mesh mesh(vertices, sizeof(vertices) / sizeof(vertices[0]));

如果按1个参数来调用，没有出现正确结果

Mesh mesh(vertices);

按照原本的设想，希望能省一个参数,没有达到目的，不知问题出在哪？

Answer 1

Mesh::Mesh(Vertex* vertices) 的形参是指针，调用 sizeof 并不能得到数组的 size，而是得到指针的 size。所以 sizeof(vertices) - 1 并不能得到你预期的值。