share a struct in c++ and c?

Question

say a define a struct in header file of c++, foo.h

typedef struct {
    ...
}foo;

in .c file I include the foo.h, then

foo* fooPtr;

will it work?

Answer 1

It depends a lot on what is actually in the struct foo. If the struct is simply data and has no behavior itself or in any of it's member fields then it should work just fine in C or C++. If it has any type of explicit or implicit behavior (think generated destructors) then no it won't work properly in C.

For example:

// Works fine in C or C++ irrespective of where it was defined 
typedef struct { 
  int field1;
} foo;

// Will have different behavior if it compiles at all.
struct bar { 
  ~bar() {
    // destructor code
  }
};

typedef struct { 
  bar b; 
} foo;

Answer 2

The C++ struct declaration is compliant with the C language as long as it does not have any C++ features; a plain, C language, declaration. For example, no private declarations.