Conflicting declarations in XC8 when using extern struct

Question

I have a variable that is a struct, defined in a .c file:

struct {
    int write_cursor;
    int read_cursor;
    message messages[10];
} out_messages = {0, 0};

To make it available in other files I have an .h file with:

extern struct {
    int write_cursor;
    int read_cursor;
    message messages[10];
} out_messages;

This worked with the Microchip C18 compiler. The XC8 compiler gives an error:

communications.c:24: error: type redeclared
communications.c:24: error: conflicting declarations for variable "out_messages" (communications.h:50)

Answer 1

The notation isn't correct, you can do:

typedef struct {
    int write_cursor;
    int read_cursor;
    message messages[10];
} Struct_out_messages;

extern Struct_out_messages out_messages;

and in a .c make the initialization.

Struct_out_messages out_messages = {0, 0, {0}};

This compiles in XC16 without any problem, hope it does also on XC8.

Answer 2

If you need to access the contents of the struct in multiple files, you could change the declaration in the header file to:

struct out_messages_t {
    int write_cursor;
    int read_cursor;
    message messages[10];
};

extern struct out_messages_t out_messages;

and then in your .c file, define and initialise:

struct out_messages_t out_messages = {0, 0};

(and include the header)