/*變量p用來(lái)存放自己定義的環(huán)境變量,而pt用來(lái)存放系統(tǒng)環(huán)境變量的PATH值
注意:此例應(yīng)該先判斷變量的返回值是否為空
取得環(huán)境變量函數(shù)的格式如下:
?char* getenv(const char *name);?return value for environment name.
?
?int putenv(const char* str);?change or add value to environment.
*/
#include <stdlib.h>
#include <iostream>
using namespace std;

int main(){
?char *p = NULL;
?char *pt=NULL;
?
?p = getenv( "AAA" );
?pt =getenv("PATH");
?
?if( p == NULL )
??cout<<"No such env named AAA"<<endl;
?else
??cout<<"AAA=" << p << endl;
?if( pt == NULL )
??cout<<"No such env named PATH"<<endl;
?else
??cout<<"PATH=" << pt<< endl;
?putenv( "AAA=123456" );
?cout<<"AAA=" << getenv( "AAA" ) << endl;
?putenv("AAA=123");
?cout<<"AAA="<<getenv("AAA")<<endl;
?
?cout<<"PATH="<<getenv("PATH")<<endl;
?return 0 ;
}

/*問(wèn)題:
?假如環(huán)境變量YU在用戶(hù)的shell下的值是123456,在我們的應(yīng)用程序中
?通過(guò)getenv()和putenv()來(lái)更改該環(huán)境變量為abcdef,那么當(dāng)我們結(jié)束應(yīng)用
?程序后回到shell下時(shí),我們用命令echo $YU,那么結(jié)果應(yīng)該是什么?
*/