CODEWITHSUNDEEP
c++incomplete-type
monolith
monolith

Reputation: 1706

'Incomplete type' of struct

I have defined a particle class Particle in a .hpp file like this 

#ifndef PARTICLE_HPP
#define PARTICLE_HPP
#include <glm/glm.hpp>
#include <GL/glew.h>
#include <GL/gl.h>

#include <vector>

struct Particle
{
    Particle()
        : m_Position(0.0f)
        , m_Velocity(0.0f)
        , m_Color(1.0f)
        , m_fRotate(0.0f)
        , m_fAge(0.0f)
        , m_fLifeSpan(0.0f)
        , m_is_alive(false)
    {}
public:
    glm::vec3   m_Position; // Center point of particle
    glm::vec3   m_Velocity; // Current particle velocity
    glm::vec4   m_Color;    // Particle color
    GLfloat     m_fRotate;  // Rotate the particle the center
    GLfloat     m_fSize;    // Size of the particle
    GLfloat     m_fAge; 
    GLfloat     m_fLifeSpan; 
    bool        m_is_alive;

};

In another .cpp file i declared Particle in typedef namespace. What i am trying to do is instantiate Particle struct and push them in a vector. Since i have an empty constructor i believe instantiating with just Particle() should work. However, i could not do it because the compile argues there is 'incomplete type not allowed' error in the bolded line. particles.push_back(Particle());

#include "Particle.hpp"
#include <stdlib.h> //malloc
#include <iostream>

#include <GL/glew.h>
#include <GL/freeglut.h>

#include<vector>

typedef struct Particle Particle;
typedef std::vector<Particle> ParticleBuffer;
ParticleBuffer particles;


int main(){
    GLuint nr_particles = 100; 

    for (GLuint i = 0; i < nr_particles; ++i) {
        particles.push_back(Particle());
    }


}

Solution

Using typedef had omitted the real problem, and that is in 

typedef struct Y Particle;

Here Y wasn't ever defined, as I believed it was pulling the definition from the header (.hpp) file, but for some reason Microsoft Visual Studio (which i was using to compile & build) didn't link the header file, but gave no errors. Instead, it just behaved like Y doesn't exist and if we look at the definition of 'incomplete type':

Structure, union, or enumerations that have no definition

The error made sense now. The "workaround" solution was to use .h file instead of .hpp, so it would get linked. Also as @YSC pointed out in accepted answer, there is no need to use typedef, as the definition is correctly pulled from .h file it should give no errors.

Upvotes: 0

Views: 1013

Answers (1)

YSC
YSC

Reputation: 40070

Your typedefs are not needed, not wanted, and break things. Indeed, typedef struct Particle Particle; is a C-ism. In C++, struct x {...}; introduces the name x in the scope, no need to prefix it with struct.

Keep it simple:

#include <vector>

struct Particle { /* ... */ }; // in real life, this is defined in a separate file
std::vector<Particle> GlobalVariablesAreEvil;

int main()
{
    GlobalVariablesAreEvil.push_back(Particle{});
}

Live demo.

Upvotes: 8

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