CODEWITHSUNDEEP
c++
Peter Stpme
Peter Stpme

Reputation: 71

C++ alignment structures

Its open season on #defines and other macros and I was looking at a portable way of aligning structures 32 bit and 64 bit code. Previously the code had a #define AMD64 and padding was added when this was not the case.

Is this a portable way of doing the same, minus the #if !defined(...) ... #endif

constexpr size_t defaultAlignmentBits = 4u;
constexpr size_t defaultAlignmentBytes = 16u;

template<size_t padLen>
struct PadIfNonZero {
    uint8_t pad[padLen];
};
template<>
    struct PadIfNonZero<0> {
};

template<typename T>
using PadToAlignment = PadIfNonZero<(sizeof(T) % defaultAlignmentBytes == 0 ? 0  : defaultAlignmentBytes - sizeof(T) % defaultAlignmentBytes)>;

And how can this be improved?

Upvotes: 0

Views: 62

Answers (1)

DrCoco
DrCoco

Reputation: 48

If you want your classes and structs to have a certain alignment in memory you should look into the alignas operator. It works like this:

Class Foo
alignas(64)
{
     Foo();
     ~Foo();
};

Here the class Foo is aligned to 64 bytes. But note that alignas is only available in c++11 or above. Hope this helps!

Upvotes: 2

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