Biegral Blog

       内存对齐， 大家应该都听说过， 我们直接来看程序：

#include <iostream>
using namespace std;

struct 
{
	int a;
	short b;
}A;

struct 
{
	short b;
	int a;
}B;

struct 
{
	short b;
	short c;
	int a;
}C;

struct 
{
	bool b;
	bool c;
	int a;
}D;

struct 
{
	bool c;
	int a;
	bool b;
}E;

struct 
{
	double a;
	int b;
	float c;
	char d;
	char f;
}F;

int main()
{
	cout << sizeof(A) << endl; // 8
	cout << sizeof(B) << endl; // 8
	cout << sizeof(C) << endl; // 8
	cout << sizeof(D) << endl; // 8
	cout << sizeof(E) << endl; // 12
	cout << sizeof(F) << endl; // 24

	return 0;
}

      继续看：

#include <iostream>
using namespace std;

#pragma pack(1)

struct 
{
	int a;
	short b;
}A;

struct 
{
	short b;
	int a;
}B;

struct 
{
	short b;
	short c;
	int a;
}C;

struct 
{
	bool b;
	bool c;
	int a;
}D;

struct 
{
	bool c;
	int a;
	bool b;
}E;

struct 
{
	double a;
	int b;
	float c;
	char d;
	char f;
}F;

int main()
{
	cout << sizeof(A) << endl; // 6
	cout << sizeof(B) << endl; // 6
	cout << sizeof(C) << endl; // 8
	cout << sizeof(D) << endl; // 6
	cout << sizeof(E) << endl; // 6
	cout << sizeof(F) << endl; // 18

	return 0;
}

      继续看：

#include <iostream>
using namespace std;

#pragma pack(2)

struct 
{
	int a;
	short b;
}A;

struct 
{
	short b;
	int a;
}B;

struct 
{
	short b;
	short c;
	int a;
}C;

struct 
{
	bool b;
	bool c;
	int a;
}D;

struct 
{
	bool c;
	int a;
	bool b;
}E;

struct 
{
	double a;
	int b;
	float c;
	char d;
	char f;
}F;

int main()
{
	cout << sizeof(A) << endl; // 6
	cout << sizeof(B) << endl; // 6
	cout << sizeof(C) << endl; // 8
	cout << sizeof(D) << endl; // 6
	cout << sizeof(E) << endl; // 8
	cout << sizeof(F) << endl; // 18

	return 0;
}

     继续看：

#include <iostream>
using namespace std;

#pragma pack(3)

struct 
{
	int a;
	short b;
}A;

struct 
{
	short b;
	int a;
}B;

struct 
{
	short b;
	short c;
	int a;
}C;

struct 
{
	bool b;
	bool c;
	int a;
}D;

struct 
{
	bool c;
	int a;
	bool b;
}E;

struct 
{
	double a;
	int b;
	float c;
	char d;
	char f;
}F;

int main()
{
	cout << sizeof(A) << endl; // 8
	cout << sizeof(B) << endl; // 8
	cout << sizeof(C) << endl; // 8
	cout << sizeof(D) << endl; // 8
	cout << sizeof(E) << endl; // 12
	cout << sizeof(F) << endl; // 24

	return 0;
}

       此时， 我们得到 warning C4086: expected pragma parameter to be '1', '2', '4', '8', or '16'

        好吧， 消化了上面的程序， 内存对其基本算是入门了。