invalid use of undefined type 'const struct ...'

Question

main.c

#include <stdio.h>
#include "constants.h"

void main()
{
    printf("%hu", MOTORs_PINs.motor_right.terminal_1);
}

constants.c

#include "constants.h"

struct __MOTOR_PIN
{
    unsigned short int terminal_1;
    unsigned short int terminal_2;
};
struct __MOTORs_PIN
{
    struct __MOTOR_PIN motor_right;
    struct __MOTOR_PIN motor_left;
};

const __MOTORs_PIN MOTORs_PINs = {.motor_right.terminal_1 = 16,
                                  .motor_right.terminal_2 = 17,
                                  .motor_left.terminal_1 = 18,
                                  .motor_left.terminal_2 = 19};

constants.h

extern const struct __MOTORs_PIN MOTORs_PINs;

error

main.c: In function 'main':
main.c:7:30: error: invalid use of undefined type 'const struct __MOTORs_PIN'
    7 |     printf("%hu", MOTORs_PINs.motor_right.terminal_1);
      |                              ^

in the above-provided code, I'm getting error about invalid use of undefined type when I was using a constant nested struct.

Note: All files are in the same directory.

Actually, I want to keep all the constants of the project in the same file that's why I want it to work in a manner that whenever I use variable MOTORs_PINs.motor_right.terminal_1 its constant value i.e. 16 should be received.

Does this answer your question? [undefined C struct forward declaration](https://stackoverflow.com/questions/621356/undefined-c-struct-forward-declaration) — tinman, Oct 09 '22 at 11:56
It would be great if you explain it with respect to my code. — Aman Rathore, Oct 09 '22 at 13:50
Your port.h file only contains “struct port_t;” but does not define that structure. Each C file is compiled independently so definitions in one (port.c) are not seen by another (main.c). — tinman, Oct 10 '22 at 19:46

invalid use of undefined type 'const struct ...'

0 Answers0