#pragma pack(show) with GCC - c++

Question

Is there a way to show the memory "pack" size with GCC ?
In Microsoft Visual C++, I am using:
#pragma pack(show)
which displays the value in a warning message; see Microsoft's documentation.
What is the equivalent with GCC?

Answer 1

Since I can't see such functionality listed in the pertinent documentation, I'm going to conclude that GCC cannot do this.

Answer 2

I use a static assertion whenever I pack a structure and want to see its size.
/*
The static_assert macro will generate an error at compile-time, if the predicate is false
but will only work for predicates that are resolvable at compile-time!
E.g.: to assert the size of a data structure, static_assert(sizeof(struct_t) == 10)
*/
#define STATIC_ASSERT(COND,MSG) typedef char static_assertion_##MSG[(!!(COND))*2-1]
/* token pasting madness: */
#define COMPILE_TIME_ASSERT3(X,L) STATIC_ASSERT(X,at_line_##L) /* add line-number to error message for better warnings, especially GCC will tell the name of the variable as well */
#define COMPILE_TIME_ASSERT2(X,L) COMPILE_TIME_ASSERT3(X, L) /* expand line-number */
#define static_assert(X) COMPILE_TIME_ASSERT2(X, __LINE__) /* call with line-number macro */
#define PACKED __attribute__ ((gcc_struct, __packed__))
typedef struct {
uint8_t bytes[3];
uint32_t looong;
} PACKED struct_t;
static_assert(sizeof(struct_t) == 7);
This will give you a compile time warning whenever the static assertion fails.