C和C ++头文件：在另一个结构内部定义全局结构

Question

I have some C code that has some structs that looks like this:

typedef struct my_library_a_t my_library_a_t;
typedef struct my_library_b_t my_library_b_t;
typedef struct my_library_c_t my_library_c_t;

struct my_library_a_t {
    struct my_library_b_t {
        int data;
        struct my_library_c_t {
            int data;
        } c;
    } b;
    int data;
};

This doesn't work in C++, because in C struct my_library_b_t defines a global struct my_library_b_t , whereas in C++ it defines ::my_library_a_t::my_library_b_t .

How can I get the inner struct definition to define a global struct in C++? Or even just not have to change too much code for it to work (I don't mind having a #ifdef __cplusplus block, but I don't want to pull the structs out because the reason they are nested in the first place is that they are used only one time each, and it's really hard to read when the inner class definitions are above the outer class definitions)

I tried struct ::my_library_b_t in the definition, but this doesn't work.

For context, I'm parsing a string that has a definition that would look like this:

a     = b "," data
b     = data "," c
c     = data
data  = %x31-39 *DIGIT  ; 1-9 followed by *(0-9)
      / "0"

And the intermediate parts have meaning, so it's useful to be able to have functions that take my_library_b_t* or my_library_c_t* .

I would prefer to have a solution that looks like this:

#ifdef __cplusplus
#define GLOBAL_STRUCT(name) ???  (I tried `:: name`)
extern "C" {
#else
#define GLOBAL_STRUCT(name) name
#endif

struct my_library_a_t {
    struct GLOBAL_STRUCT(my_library_b_t) {
// ...

Answer 1

I recommend this

struct my_library_a_t {
    struct my_library_b_t {
        int data;
        struct my_library_c_t {
            int data;
        } c;
    } b;
    int data;
};
#ifdef __cplusplus
    typedef struct my_library_a_t::my_library_b_t my_library_b_t;
    typedef struct my_library_b_t::my_library_c_t my_library_c_t;
#else
    typedef struct my_library_a_t my_library_a_t;
    typedef struct my_library_b_t my_library_b_t;
    typedef struct my_library_c_t my_library_c_t;
#endif

Notice that after alias my_library_b_t, you don't need to use my_library_a_t::my_library_b_t::my_library_c_t