[SOLVED] unresolved external symbol for structures in cpp?

unresolved external symbol for structures in cpp?

I know most of time you get UNRESOLVED EXTERNAL SYMBOL for not including library or for not correctly defining function in class, but i get same error for structure. I have few files .cpp and .h in one of the .h i have defined

extern struct MyDataStruct StructData;

I include this .h in my .cpp file but i get

'struct MyDataStruct StructData' unresolved external symbol

I define this structure out of any class and i access it without any class prefix.

Solution

You need to actually define it in one and one only .cpp file ie allocate some space in the object file for it e.g.

struct MyDataStruct StructData;

Note in this case there is no extern.

Whilst all other code accesses it through the declaration in the header which retains the extern - which tells the compiler and linker that somewhere else in the executable there is something to resolve the reference.