Question

I have a strange problem in C about including header files.

main.c

#include <stdio.h>
#include <stdlib.h>
#include "location.h"

int waste_new_line();

int main()
{
    location *crossroads = malloc(sizeof(*crossroads));
...

location.h

typedef struct Location_Struct location;

location.c

typedef struct Location_Struct {
    int ID;
    char *name;
    char *description;
} location;

int setup_location(location* l, char* name)
{
    ...

Now this isn’t working because

location *crossroads = malloc(sizeof(*crossroads));

is throwing an error:dereferencing pointer to incomplete type meaning that it can see the contents of location.h, yet it doesn’t seem to be aware of location.c…

I’ve looked around and all the tutorials I’ve seen say that the linker will link both files together.

EDIT:

I have altered the code to include an initializer inside location.c as so:

main.c

...
#include "location.h"

int waste_new_line();

int main()
{

    location *crossroads = initialize_location();
    ....

location.h

typedef struct Location_Struct location;

location* initialize_location();

location.c

...
typedef struct Location_Struct {
    int ID;
    char *name;
    char *description;
} location;

location* initialize_location(location* l)
{
    return malloc(sizeof(location));
}
...

This is still throwing the same error, yet only when I try and access the members of crossroads using:

crossroads->description

this will throw the deferencing to incomplete type error.

EDIT 2: For now I’ve decided to just put the struct definition in the header file…

Answer 1

This behaviour is expected. When you #include "location.h", only the header file is visible to the compiler. The location.c file comes along later, at link time.

You have two options:

1. Add a function, which you declare in location.h and define in location.c, which does the necessary malloc and returns a pointer.
2. Move the full definition of the struct to the header file.