Structure Declaration

[r_james14]

Hi There,

I have a .h file that is accessed by two different .c file

in my .h file I need a structure such as

struct {
int mph;
int distance;
int numberofpeople;
} car[8];

and in both .c files, for example

car[0].mph = 100;

how do i define the strcture,

currently i keep getting an error of
"multiply-defined:......"

thanks

[Salem]

In the .h file, you need

struct cartype {
int mph;
int distance;
int numberofpeople;
} 

extern struct cartype car[8];

In ONE of the .c files, you have
struct cartype car[8];

[hk_mp5kpdw]

The reason you get the error is that the header file declares an array of structs that becomes included in both source files. Both source files have a struct cartype car[8] array. When you try to link, the linker complains that you have this same array declared in two different source files. The struct definition needs to be visible to both source files but the actual declaration of the array can only be in one of those source files. This is what Salem's post above addresses.

The extern declaration lets both source files know that there is an array that exists (somewhere, as Salem mentions it should only be in one of the source files) but does not actually cause any space to get allocated in either source file when the header is included. This allows the source file that does not actually contain the true array declaration know about it and properly take it into account when compiling.

PS, I think Salem missed a semicolon at the end of the struct definition.

[r_james14]

hi guys,

thanks for the responses, got the problem solved but also taught me how and why,
thanks again