C ++ / CLI结构/类对齐

Question

It seems I cannot make C++/CLI structures be aligned with less than 8 bytes. I have a struct of two Int32, allocate a million of them, and voilà: 16 MB memory according to ".NET Memory Profiler" (plus the list data). I set the compiler option to /Zp4 (also tried /Zp1), to Minimize Size (/O1) and Small Code (/Os), just to make sure, I additionally put a "#pragma pack(1)" into my code, to no avail. My struct is still taking up 16 Bytes. I changed it to class, still the same.

Why that? How to change?

Ciao, Eike

using namespace System;
#pragma pack(1)

ref struct myStruct
{
    Int32 a;
    Int32 b;
};

int main(array<System::String ^> ^args)
{
    System::Collections::Generic::List<myStruct^> list;
    for (int i = 0; i < 1000000; i++)
    {
        list.Add(gcnew myStruct());
    }
    // avoid optimization
    Console::WriteLine(list[333333]->a);
    return 0;
}

Answer 1

You need to use value types to be able to specify alignment. Beyond that I'm not sure this is the best way to measure this. Reference types also have some small built in overhead. Try value struct/value class instead.