初始typedef结构指针（C / C ++）

Question

If I define a struct like below

typedef struct Coder {
    float **data;
};

For my convenience, I also define a pointer to this struct

typedef Coder *AUTO;

and then I have to initial it by calling

AUTO  myInstance = new Coder;

My problem appear when I call

myInstance->data= NULL;

The VC 2010 told me that there was no type specifier. I don't understand what problem is here. Could you please help me?

Answer 1

If you are in C++ , just do :

struct Coder
{
    float **data;
};

typedef Coder *AUTO;

Also you have to be sure that the AUTO declaration is done after the declaration of your struct or you can forward-declare your struct .

---

Also, it is possible that NULL is undefined.

You can replace it by 0 or just look at the link I just gave you.

Here is a live example .

---

EDIT : The code you gave us cannot work :

#include <tchar.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <conio.h>
#include <iostream>

struct Coder {
        float **data; // 2-D matrix
};
typedef Coder *AUTO;

AUTO  myFeatures = new Coder;

myFeatures->data = NULL; // Forbidden

int main (){
        myFeatures->data = new float *[2];
        myFeatures->data[0] = new float [2];
}

You can only have declaration in namespace scope, not expression like that.

In §7.3.1/1 of the standard :

namespace-body:
declaration-seq _opt

which says the namespace-body can optionally contain only declaration .

This code will work :

// Your includes

struct Coder {
        Coder() : data(NULL) {} // Constructor who initialize data to NULL
                                // via the member-initialization-list

        float **data; // 2-D matrix
};
typedef Coder *AUTO;

AUTO  myFeatures = new Coder; // Do you want to keep it in global ??
                              // It's not a really good design

int main (){
        // You should put your declaration here.

        // myFeatures->data = NULL; useless now
        myFeatures->data = new float *[2];
        myFeatures->data[0] = new float [2];
}

Answer 2

In C typedef:

typedef int mango;

Now your mango represent "int" datatype.

user defined struct syntax:

struct mystruct;

use typedef:

typedef struct mystruct newtype;

Now newtype represent your struct mystruct.

Your the typedef name is missing,

typedef struct Coder {
    float **data;
}Coder ;

Answer 3

typedef struct Coder {
    float **data;
}Coder;

will be ok.