How do include header files function

Question

Ok, so how I understand #include works is by looking up what you are including and complies that and replaces it where the include is. however, when I assume this, my program doesn't compile and it gives __ is undefined all over the place.

for example when in my main.c will have something like

#include "tim.h"
#include "tim_cfg.h"
#include "tim_api.h"

tim.h contains some typesdefs like

typedef enum
{
RATE_DIV1 = 0X0,
RATE_DIV2 = 0X1,
RATE_DIV3 = 0X2,
RATE_DIV4 = 0X3,
RATE_DIV5 = 0X4,
RATE_DIV6 = 0X5,
RATE_DIV7 = 0X6,
RATE_DIV8 = 0X7,
RATE_DIV9 = 0X8
} BaseRate_T;

typedef unsigned char byte;

tim_cfg.h contains register locations and basic structs

typedef struct
{
byte  TimerSize;         
byte  InterruptLevel;    
} TIMInfo_T;

and tim_api.h contains the function prototypes of the tim functions

So, the problem is why do I get errors

identifier "byte" is undefined

When it the first thing I include?

shouldnt the typedef take care of the error which is included in the first include — Chrusciki
– Chrusciki, Commented Mar 28, 2014 at 19:46
Does tim.h also itself include tim_api.h at a point before where the typedef is? If it's not too long, post the entire tim.h, or at least the portion up to and including TIMInfo_T. — TypeIA
– TypeIA, Commented Mar 28, 2014 at 20:04
If you reduce it to just the typedef, the struct, and a main program (to print sizeof(TIMInfo_T), say), it works fine, so something else is going on. Does tim_api.h have code in it? That sometimes has weird effects. — John C
– John C, Commented Mar 28, 2014 at 23:06

paxdiablo · Accepted Answer · 2015-04-14 04:52:00Z

1

You should follow the rule that every header file should include what it needs to work.

With the setup you have, if someone includes tim_cfg.h on its own, the byte type is not defined.

A better solution would be:

tim_cfg.h:
    #include "tim.h"
    typedef struct
    {
        byte  TimerSize;         
        byte  InterruptLevel;    
    } TIMInfo_T;

That way, everything that is needed for tim.cfg.h is there when you include it.

answered Apr 14, 2015 at 4:52

paxdiablo

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