How to initialize a vector in a struct in c++

Question

I am having a problem with vectors in c++. I am new to c++ so keep this in mind please.

So I have the following struct in the begining of my program:

typedef struct grupo
{
    float transX, transY, transZ, rotX, rotY, rotZ, rotAngle, scaleX, scaleY, scaleZ;
    char **modelos;
    struct grupo** grupos;
    int nNomes = 0, nGrupos=0;
    std::vector<float> vertices;
};

struct grupo *grupo;

And I just start the main like this:

grupo = (struct grupo*)malloc(sizeof(struct grupo));
grupo->modelos = (char **)malloc(sizeof(1));
grupo->grupos = (struct grupo **)malloc(sizeof(struct grupo));

And in the middle of main I am tryting to use this:

grupo->vertices.push_back(x);

But it keeps crashing the program. I am using visual studio, and using debugging mode. I can see that is when pushing X to the vector that crashes (x has a value). I've tried to change the vector to an array of floats. So the problem i can imagine is with the initialization of the vector... Can you help with what am I missing?

Thank you :)

Answer 1

You're using C++, you don't need the "new" or malloc keyword unless for specific reasons. You don't need the typedef for structs.

I'm not sure what your char** is supposed to be, but you can use std::string for strings.

Maybe what you're trying to do is this:

struct Grupo
{
    float transX, transY, transZ, rotX, rotY, rotZ, rotAngle, scaleX, scaleY, scaleZ;
    std::string modelos;
    int nNomes = 0, nGrupos=0;
    std::vector<float> vertices;
};

In main:

Grupo grupo;
grupo.vertices.push_back( ... );

Then I would advise you to read a bit more about what is exactly the C++ language and how it's not C.

Answer 2

Since you're using C++; if you want to create a grupo dynamically, you should use the new operator, with the constructor:

grupo = new grupo();

malloc does not properly initialize C++ objects such as std::vector.

---

P.S. I am not sure what the grupo->modelos and grupo->grupos are supposed to be, but I'd use proper C++ types for them (perhaps modelos should be std::string, etc). Additionally, I suspect that you've got one * too much for both modelos and grupos.

Answer 3

C++ does not need the typedef in the declaration.

To properly initialize a structure, you should write a ctor to replace the compiler provided ctor (which generally does nothing).

Something like the following (with just a few attributes):

struct grupo
{
   float transX, transY;
   // ...
   int nNomes;
   int nGrupos;
   std::vector<float> vertices;

   // I prefer initialization list form
   grupo() : transX(0.0),
             transY(1.0),
             // ...
             nNomes(0),
             nGrupos(0)
             // vertices default ctor is ok, creates empty vector
      {
         // use vertices.push_back(...); to fill vertices
      }

};

grupo grupo;

Next you will want to write a more useful ctor, one with parameters to use (instead of the literal constants), such that you could build multiple grupo.

grupo grupo1(1.0, 2.0, 3, 4);
grupo grupo2(3.0, 4.0, 5, 6);
// etc.