Multiple Source Files with Structures

i have a big favour to ask, could sombody please give me an example of multiple source files using structures. the reason is that i have a rather large file with 1k+ lines and roughly 18 functions, all in 1 source file.

i have tried before but kept getting "multiple definition" errors and a few others i cant remember, as i kept deleting the projects and adding to my other. i have managed to get functions working in different files before quite comfortably with functions, however i cant seem to manage it with structures.


thanks,

this goes into the header

Code:

---

#ifndef STRUCT_EXAMPLE_H
#define STRUCT_EXAMPLE_H

typedef struct example_tag
{
  int x;
}example;

int fillstruct(example* var);
#endif

---

This goes into the c-file

Code:

---

#include "struct_example.h"
int fillstruct(example* var)
{
  if(var) var->x = 5.0;
  return 0;
}

---

in this case you can have several c-files using the struct without the problem

PS. hope you don't use global vars

Quote:

---

Originally Posted by vart

this goes into the header

Code:

---

#ifndef STRUCT_EXAMPLE_H
#define STRUCT_EXAMPLE_H

typedef struct example_tag
{
  int x;
}example;

int fillstruct(example* var);
#endif

---

This goes into the c-file

Code:

---

#include "struct_example.h"
int fillstruct(example* var)
{
  if(var) var->x = 5.0;
  return 0;
}

---

in this case you can have several c-files using the struct without the problem

PS. hope you don't use global vars

---

so the structure goes in the headerfile, and the rest in the .cpp file?

> the reason is that i have a rather large file with 1k+ lines and roughly 18 functions, all in 1 source file.

This is not a large file by any means. So don't worry much with breaking it up. Unless of course, the file contains unrelated code. A good rule of thumb is to divide your source files so that each file contains code that is somehow related.

> i have tried before but kept getting "multiple definition" errors and a few others i cant remember,

Some things can make this happen. If you are trying to include a source file (.cpp, .c,...) into other sources files, for instance. Or if you are coding definitions inside a header file (.hpp, .h,...). Header files should not contain any definitions (with a few exceptions like class and structure definitions, iniline function definitions, const definitions).

> however i cant seem to manage it with structures.

Is it possible that you are defining your structures like this?

Code:

---

struct SomeStruct {
    /* ... */
} foo;

---

By doing it you are both defining the struct SomeStruct (which is valid inside an header file), and defining a variable called foo that is of type SomeStruct. That will create you problems when trying to include the header file in more than one source file. You will get a multiple-definitions error of foo.

could you explain why it has typedef and i take it exmple_tag is the name of the structure?

Quote:

---

Originally Posted by Mario F.

> the reason is that i have a rather large file with 1k+ lines and roughly 18 functions, all in 1 source file.

This is not a large file by any means. So don't worry much with breaking it up. Unless of course, the file contains unrelated code. A good rule of thumb is to divide your source files so that each file contains code that is somehow related.

> i have tried before but kept getting "multiple definition" errors and a few others i cant remember,

Some things can make this happen. If you are trying to include a source file (.cpp, .c,...) into other sources files, for instance. Or if you are coding definitions inside a header file (.hpp, .h,...). Header files should not contain any definitions (with a few exceptions like class and structure definitions, iniline function definitions, const definitions).

> however i cant seem to manage it with structures.

Is it possible that you are defining your structures like this?

Code:

---

struct SomeStruct {
    /* ... */
} foo;

---

By doing it you are both defining the struct SomeStruct (which is valid inside an header file), and defining a variable called foo that is of type SomeStruct. That will create you problems when trying to include the header file in more than one source file. You will get a multiple-definitions error of foo.

---

the reason is that it is tedious to work on as i have to keep scrolling up and down all the time, as im not an experienced programmer. and that its rather difficult to find the correct funtion i want to work on.

i had my structure declared in the header file as

Code:

---

struct somestruct
{
int x;
};

somestruct mystruct[5];

---

anyway it doesnt matter, ill just keep it in one source file.

Quote:

---

Originally Posted by dac

could you explain why it has typedef and i take it exmple_tag is the name of the structure?

---

it's because I'm regular with using structs in C...
there - you cannot use struct name without struct keyword if you don't typedef it previously...

in C++ classes are mostly used...