How to solve Undefined Struct in C? - c

Question

I've been at this for several days now, unable to compile successfully. I made a very-oversimplified project separate from my main one. Depending which embeded struct I comment out, I get one of the following errors:
file: x2d_gfx_speech_balloon.h
error C2079: 'sprBalloon' uses undefined struct 'X2D_SPRITE'
error C2079: 'font' uses undefined struct 'X2D_FONT'
Side note: Putting the sprite and font headers from the common header into the speech balloon header itself has no effect either.
I'm going to provide the entire simplified code below. Please let me know if you see any syntax wrong, and optionally, feel free to compile it on your side if it helps. My environment is Windows 7 with Visual Studio 2010 and using C89.
main.c
#include "common.h"
int main(void)
{
return 0;
}
common.h
#ifndef _COMMON_H_
#define _COMMON_H_
#include <stdio.h>
#include <stdlib.h>
#include "constants.h"
#include "X2D_GFX_Sprite.h"
#include "X2D_GFX_Font.h"
#include "X2D_GFX_Speech_Balloon.h"
#endif
constants.h
#ifndef _CONSTANTS_H_
#define _CONSTANTS_H_
/* General Constants */
#define TRUE 1
#define FALSE 0
#endif
X2D_GFX_Font.h
#ifndef _X2D_GFX_FONT_H_
#define _X2D_GFX_FONT_H_
#include "common.h"
/* Font Structure */
struct X2D_FONT
{
float x, y;
int size;
int blnShow;
};
/* Font Prototypes (not shown here)... */
int fnt_init(struct X2D_FONT *objFont, const char *strFileName,
const char *strText, const float x, const float y,
const unsigned int size);
#endif
X2D_GFX_Font.c
#include "X2D_GFX_Font.h"
int fnt_init(struct X2D_FONT *objFont, const char *strFileName,
const char *strText, const float x, const float y,
const unsigned int size)
{
return TRUE;
}
X2D_GFX_Sprite.h
#ifndef _X2D_GFX_SPRITE_H_
#define _X2D_GFX_SPRITE_H_
#define MAX_VARSI 10
#include "common.h"
struct X2D_SPRITE
{
float x;
float y;
unsigned int width;
unsigned int height;
int blnShow;
float vx, vy;
float angle;
int varsi[MAX_VARSI];
};
int spr_init(struct X2D_SPRITE *spr, const char *strFileName);
#endif
X2D_GFX_Sprite.c
#include "X2D_GFX_Sprite.h"
int spr_init(struct X2D_SPRITE *spr, const char *strFileName)
{
return TRUE;
}
X2D_GFX_SPEECH_BALLOON.h
#ifndef _X2D_GFX_SPEECH_BALLOON_H_
#define _X2D_GFX_SPEECH_BALLOON_H_
#include "common.h"
/* Contains a list of acceptable balloon types */
enum ESpeechBalloonType
{
ESpeechBalloonType_Talk,
ESpeechBalloonType_Thought,
ESpeechBalloonType_Yell,
ESpeechBalloonType_Whisper
};
/* Speech Balloon types */
struct X2D_SPEECH_BALLOON
{
struct X2D_SPRITE sprBalloon;
struct X2D_FONT font;
enum ESpeechBalloonType eBalloonType;
};
#endif
X2D_GFX_SPEECH_BUBBLE.c
#include "X2D_GFX_SPEECH_BALLOON.h"

Answer 1

Your issue is the order in which files are included, specifically in X2D_GFX_Sprite.c. If you run just the preprocessor on that file (in Linux you can use cpp or gcc -E, I don't know how in Windows) and scroll down to the very end, you'll find that the X2D_SPRITE struct is being declared after it's used:
struct X2D_SPEECH_BALLOON
{
struct X2D_SPRITE sprBalloon;
struct X2D_FONT font;
enum ESpeechBalloonType eBalloonType;
};
# 11 "common.h" 2
# 7 "X2D_GFX_Sprite.h" 2
struct X2D_SPRITE
{
float x;
float y;
unsigned int width;
unsigned int height;
int blnShow;
float vx, vy;
float angle;
int varsi[10];
};
Two easiest ways to fix it would be to either not use common.h or move #include "common.h" after the struct declaration in X2D_GFX_Sprite.h.
This happens because X2D_GFX_Sprite.c includes X2D_GFX_Sprite.h, which includes common.h, which includes the other .h files. The preprocessor first copies in X2D_GFX_Sprite.h. When it finds #include "common.h", it begins copying that file. The first three includes are copied in. When it gets back to X2D_GFX_Sprite.h, it'll copy it in, but the header guards will get rid of everything in it. Next, it copies in X2D_GFX_Font.h and X2D_GFX_Speech_Balloon.h, which includes the X2D_SPEECH_BALLOON struct, in that order. Only then does it finally add in the rest of X2D_GFX_Sprite.h, including the X2D_SPRITE struct. This results in the two structs not being copied in the correct order.