环境变量操作

 #include <stdio.h>
  2 #include <stdlib.h>
  3 
  4 int main(int argc,char **argv,char **env)
  5 {
  6    extern char **environ;  //得到环境变量的首地址
  7 
  8    printf("env=%p,environ=%p\n",env,environ);
  9 
 10    char *value=getenv("LANG");
 11    printf("value=%s\n",value);
 12 
 13    /*改变环境变量*/
 14    putenv("VAR=abc");
 15    putenv("LANG=xxx");
 16    printf("LANG=%s\n",getenv("LANG"));
 17    setenv("VAR","123",0);   //参数为0,不改变
 18    printf("VAR=%s\n",getenv("VAR"));
 19    setenv("VAR","123",1); //参数为1,改变
 20    printf("VAR=%s\n",getenv("VAR"));
 21 
 22    //删除环境变量
 23    unsetenv("VAR");
 24    printf("VAR=%s\n",getenv("VAR"));
 25    clearenv();
 26    printf("HOME=%s\n",getenv("HOME"));
 27    printf("PATH=%s\n",getenv("PATH"));
 28 
 29    return 0;
 30 }
~