注意include .h 文件的使用

场景

（看到项目中有如下使用方式，觉得会存在弊端，占用不必要的内存，虽然结果没有问题。）

多个变量定义在一个fid.h文件，

多个cpp文件（比如100个）同时#include "fid.h"

弊端

任意一变量会在cpp文件中展开，如果fid.h被include了100次，任一fid.h中的变量将在可执行文件中定义100次，
之所以链接不会出错重复定义，是因为变量被const修饰后，变为内链接。

</pre>fid.h<pre name="code" class="cpp">#ifndef _FID_H_
#define _FID_H_

//----------------------  Account  -----------------------------
const int FID_ACCOUNT_BASE                    = 10000;
const int FID_ACCOUNT_ID                      = FID_ACCOUNT_BASE + 0;
const int FID_ACCOUNT_NAME                    = FID_ACCOUNT_BASE + 1;
const int FID_ACCOUNT_PASSWORD                = FID_ACCOUNT_BASE + 2;
const int FID_ACCOUNT_COMPANY_ID              = FID_ACCOUNT_BASE + 3;
const int FID_ACCOUNT_TOKEN                   = FID_ACCOUNT_BASE + 4;
const int FID_ACCOUNT_DEPARTMENT              = FID_ACCOUNT_BASE + 5;
const int FID_ACCOUNT_COMPANY_NAME            = FID_ACCOUNT_BASE + 6;
const int FID_ACCOUNT_ROLE                    = FID_ACCOUNT_BASE + 7;
const int FID_ACCOUNT_PERMISSION              = FID_ACCOUNT_BASE + 8;
const int FID_ACCOUNT_CODE					   = FID_ACCOUNT_BASE + 9;
const int FID_ACCOUNT_TELEPHONE               = FID_ACCOUNT_BASE + 10;
const int FID_ACCOUNT_PHONE		           = FID_ACCOUNT_BASE + 11;
const int FID_ACCOUNT_EMAIL				   = FID_ACCOUNT_BASE + 12;
const int FID_ACCOUNT_RM		               = FID_ACCOUNT_BASE + 13;
const int FID_ACCOUNT_MSN		               = FID_ACCOUNT_BASE + 14;
const int FID_ACCOUNT_QQ		               = FID_ACCOUNT_BASE + 15;
const int FID_ACCOUNT_ADDRESS	               = FID_ACCOUNT_BASE + 16;
const int FID_ACCOUNT_PASSWORD_ORG            = FID_ACCOUNT_BASE + 17;    

........
#endif // _FID_H_