C Defining an enum in one header file and using that enum as a function parameter in another file

Question

I have defined an enum in a header file, global.h:

Typedef enum
{
    ELEMENT1,
    ELEMENT2,
    ELEMENT3
}e_element;

I have a second file using the enum as a function parameter. file2.c

#include global.h
#include file2.h
Function(e_element x)
{
Body…
}

The prototype is in: file2.h

Function(e_element x);

The compiler doesn’t know e_element in file2.h. I have tried putting the #include for global.h in both file2.c and file2.h, but it still doesn’t see it. I would put the enum in file2.h, except that it is used by several other files, so if I move it the problem will just show up somewhere else. How can I get the file2.h prototype to see e_element?

It's typedef, not Typedef. When I fix that, and add quotes around the header files in #include, your code compiles. — Barmar
– Barmar, Commented Jul 11, 2016 at 22:11
Fix your basic syntax errors, then see if you still have the problem. — Barmar
– Barmar, Commented Jul 11, 2016 at 22:13
Your code has a lot of typographic errors. I assume this is not your real code? Please post your real code, not some kind of pseudo-code. Or, OTOH, if this is really your code, you should first read a good textbook about C. — Rudy Velthuis
– Rudy Velthuis, Commented Jul 11, 2016 at 22:14

Alden · Accepted Answer · 2016-07-11 22:22:14Z

6

This worked for me:

global.h

#ifndef GLOBAL_H
#define GLOBAL_H

typedef enum
{
    ELEMENT1,
    ELEMENT2,
    ELEMENT3
}e_element;

#endif

file2.h

#ifndef FILE_2_H
#define FILE_2_H

#include "global.h"
int test(e_element);

#endif

file2.c

#include "file2.h"

int test(e_element x)
{
    return x == ELEMENT1;
}

int main() {
    return 0;
}

edit: #ifndef is conventionally used as a "header guard". It prevents a header file from being included multiple times by the preprocessor, which prevents things from being defined multiple times. It works by checking if a unique symbol has been defined before. If it has not, then it immediately defines it and then continues with the header file until #endif. If the symbol was already defined then it skips the guarded code completely, preventing multiple definitions. An example of multiple definitions would be if the same header file was included in a source and a header that the source also includes.

See this link for more information.

edited Jul 11, 2016 at 22:22

answered Jul 11, 2016 at 22:16

Alden

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7 Comments

Barmar Over a year ago

You should explain the purpose of all those #ifndef, maybe with also include a link to a tutorial on header guards.

Alden Over a year ago

Sure. I added some more info and a link.

GJoseph Over a year ago

Sorry. The code above was done in a hurry. The actual code says "typedef" with a small t (auto-correct), and the #include files are in quotes.

GJoseph Over a year ago

global.h #ifndef SOURCES_GLOBAL_H_ #define SOURCES_GLOBAL_H_ //controller enum typedef enum { ELEMENT1, ELEMENT2, ELEMENT3 }e_controllers; #endif /* SOURCES_GLOBAL_H_ */ file1.h // I get the error in this file void setSequenceStatus(e_controllers controller, bool value); file1.c #include "file1.h" #include "global.h" void setSequenceStatus(e_controllers controller, bool value) { if(controller == FF40_MMS_DSRC_CAS) { sequence_status_FF40 = value; } }

Alden Over a year ago

From what you wrote it doesn't look like file1.h is including global.h. It must because it is using an enum from globals.h.

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