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emilbbb

A structure size problem

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Here is my code:
#include <iostream.h>

struct Test
{
	int v1;
	short v2;
	char v3;
};

int main()
{
	Test test;

	cout << "Int: " << sizeof(int) << " bytes\nShort: " << sizeof(short) << " bytes\nChar: " << sizeof(char) << " bytes\n----------" << endl;//" " << sizeof(char) << " " << sizeof(char) << endl;

	cout << "Test.v1: " << sizeof(test.v1) << " bytes\nTest.v2: " << sizeof(test.v2) << " bytes\nTest.v3: " << sizeof(test.v3) << " bytes\n----------" << endl;// " " << sizeof(test.v4) << " " << sizeof(test.v5) << endl;

	cout << "test: " << sizeof(test) << " bytes\nTest: " << sizeof(Test) << " bytes" << endl;

	return 0;
}
And the output i get is: Int: 4 bytes Short: 2 bytes Char: 1 bytes ---------- Test.v1: 4 bytes Test.v2: 2 bytes Test.v3: 1 bytes ---------- test: 8 bytes Test: 8 bytes Why does it say that the structure Test is 8 bytes when v1+v2+v3 is only 7 bytes? I have tested some other structures too. If I use this structure:
struct Test
{
	int v1;
	short v2;
	char v3;
	char v4;
};
it says that the size is 8 bytes which is correct but if I use this structure:
struct Test
{
	int v1;
	short v2;
	char v3;
	char v4;
	char v5;
};
it says that the size is 12 bytes which is not correct. I have tested to compile the program on different compilers but they all return the same wrong result. Does anyone know why it returns the wrong size of the structure? [edited by - emilbbb on September 23, 2003 11:18:27 AM]

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Heh The compiler is padding the struct to memory-align it as memory-alignement will make it faster.

I think (if you''re using Visual C++) you can use:


#pragma push(pack,1) //At the start of struct declarations
#pragma pop //At the end of struct declarations


to get the correct sizes.

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