C中的结构数组

Question

I am still learning C, despite some working programs, but now I came to structures and the pains started. I have an already working program, in XC8 under MPLABX (target is a PIC18 ), composed by a Main.c , an header and some additional .c files. In the header I already have an array of structures (font descriptors), perfectly working.

Now, I want to add a new piece of code (dynamic menus) so I made an additional header file (struct.h) with the structure and array definition, plus a new C file (menus.c) that will handle the menus; both files are included in the main.c

When I started to write the menu's rows assignements I got the following errors:

invalid dimension

and then

missing basic type; int assumed

These are the (very simplified) pieces of offending codes:

STRUCT.h

#ifndef STRUCT_H
#define STRUCT_H

typedef struct Row
{
    char *label;
    int posX;
    int posY;
};

struct Row rows[20];

#endif  /* STRUCT_H */

MENUS.c

#ifndef STRUCT_H
#include  "struct.h"
#endif

rows[0].posX = 1;

The error rises at this last row. I'm 100% sure this is a mine very stupid error, but where? Thanks

Answer 1

First of all it's not necessary to protect the include from main since it's already done from STRUCT.h

So instead of in main

#ifndef STRUCT_H
#include  "struct.h"
#endif

directly use(in main the .h is the one which should have protection which it already does, no need to do it twice)

#include  "struct.h"

Now back to your code the problem you are having is that you're not modifying the structure in a function, meaning that rows[0].posX = 1; will never be executed

This should work:

#include "struct.h"

int main(void)
{

    rows[0].posX = 1;

    //do something else like print result etc
    return 0;
}

Also you're not using the typedef, it's an empty use of typedef since you didn't put any name afterwords note these two are the same:

typedef struct Row
{
    char *label;
    int posX;
    int posY;
};



struct Row
{
    char *label;
    int posX;
    int posY;
};

I would use something along the lines of

typedef struct Row
{
    char *label;
    int posX;
    int posY;
}row_t;

Now you can directly use row_t as a data type instead of struct row

Finally I wouldn't make it a global variable I would make it local to main and pass a pointer to any function that requieres the array/membery of array

#include <stdio.h>

typedef struct Row
{
    char *label;
    int posX;
    int posY;
}row_t;


int main(void)
{

    row_t rows[20];//Not global local to main
    rows[0].posX = 1;
    printf("%d\n",rows[0].posX );
    //do something else like print result etc
    return 0;
}