Type Example (libffi: the portable foreign function interface library)

2.3.5 Type Example

The following example initializes a ffi_type object representing the tm struct from Linux’s time.h.

Here is how the struct is defined:

struct tm {
    int tm_sec;
    int tm_min;
    int tm_hour;
    int tm_mday;
    int tm_mon;
    int tm_year;
    int tm_wday;
    int tm_yday;
    int tm_isdst;
    /* Those are for future use. */
    long int __tm_gmtoff__;
    __const char *__tm_zone__;
};

Here is the corresponding code to describe this struct to libffi:

    {
      ffi_type tm_type;
      ffi_type *tm_type_elements[12];
      int i;

      tm_type.size = tm_type.alignment = 0;
      tm_type.type = FFI_TYPE_STRUCT;
      tm_type.elements = &tm_type_elements;
    
      for (i = 0; i < 9; i++)
          tm_type_elements[i] = &ffi_type_sint;

      tm_type_elements[9] = &ffi_type_slong;
      tm_type_elements[10] = &ffi_type_pointer;
      tm_type_elements[11] = NULL;

      /* tm_type can now be used to represent tm argument types and
	 return types for ffi_prep_cif() */
    }