object won't pack data - c++

Question

I'm trying to pack data in a c++ struct.
My struct has this layout:
struct structName
{
int16_t member1;
int32_t member2;
uint32_t member3;
uint32_t member4;
uint32_t member5;
etc
}__attribute__((packed));
Using offsetof($structname, $membername) I get back the correct offsets of the data (0,2,6,10,14 . . .), but when I access the data by member-name I get the data at 4 byte offsets (0,4,8,12,16 . . .) as if the struct wasn't packed.
Is
} __attribute__((packed));
the correct way to make a struct packed?
.
.

Answer 1

Update: mydogisbox wrote:
For the record, __attribute__((packed)), #pramga pack(1) and #pragma pack(push, 1) all worked.
__attribute__((packed)) is a gcc extension, which is supported.
The clang documentation says it also supports #pragma pack(...) directive:
clang has some experimental support for extensions from Microsoft
Visual C++; to enable it, use the -fms-extensions command-line option.
This is the default for Windows targets. Note that the support is
incomplete; enabling Microsoft extensions will silently drop certain
constructs (including __declspec and Microsoft-style asm statements).
clang supports the Microsoft #pragma pack feature for controlling record layout.
source: http://clang.llvm.org/docs/UsersManual.html
Just say:
#pragma pack(1)
struct my_struct {
int16_t x;
// etc.
};
to see if it works (compile with -fms-extensions if not using Windows).
Note the above are all non-standard extensions, and the new C++11 standard has a new alignas keyword: http://en.cppreference.com/w/cpp/language/alignas
struct alignas(1) my_struct {
int16_t x;
// etc.
};
but its support is still a bit sketchy.