[source lang=cpp]
#include <pshpack1.h>
template<typename T, unsigned int N>
class Array
{
protected:
T elems[N];
public:
// member access
operator const T* () const /*----*/ { return elems; }
operator T* () /*----------------*/ { return elems; }
T operator[] (int i) const /*----*/ { return elems; }
T& operator[] (int i) /*---------*/ { return elems; }
};
#include <poppack.h>
C++'s pshpack & poppack & array padding
Author
I've read around and found that C may or may not pad an array of structs to take advantage of the word length on a particular machine. I've also read that pshpack and poppack can overload the automatic type padding, and I'm wondering if this would be the correct usage of the terms to avoid type padding:
Author
Well, it isn't part of the language, yes, but I'm wondering if including pshpack.h and poppack.h would stop automatic byte-alignment...
It looks ok to me, but I'm more of a straight C programmer so I don't know how the packing impacts on the template. My comment was more germain to the title of the thread.
The distance between two consecutive elements in an array of T is sizeof(T). There is never any padding between array elements: all padding is part of T, and thus represented in sizeof(T). If you want to reduce the size of an array of T, your only possibility is to reduce the size of T itself.
So from what ToohrVyk said, wrapping the template definition in pragma packs won't make a difference. The packing needs to be applied to whatever T is.
This topic is closed to new replies.
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