#include<stdio.h>
 int main()
 {
   //libc中定义的全局变量environ指向环境变量表,environ没有包含在任何头"%s\n",*environ++);
 //  }
 //  printf("hah");
   int i = 0;
   for(i = 0;environ[i]!=NULL;i++)
   {
     printf("%s\n",environ[i]);
   }
   return 0;
 }

#include <stdlib.h>
char *getenv(const char *name);

#include <stdlib.h>
int setenv(const char *name, const char *value, int overwrite);
int unsetenv(const char *name);

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 

int main(void) 
{ 
  char* val; 
  const char* name ="ABC"; 

  //获取ABC环境变量的值 
  val = getenv(name); 
  printf("No.1 %s=%s\n", name, val); 

  //覆盖写入环境变量 
  setenv(name, "I amsure of that I will get it", 1); 
  printf("No.2%s=%s\n", name, val); 

  val = getenv(name); 
  printf("No.3%s=%s\n", name, val); 

  //删除一个环境变量 
  int ret =unsetenv("ABC"); 
  printf("ret =%d\n",ret); 

  val = getenv(name); 
  printf("No.3 %s=%s\n",name, val); 

  return 0; 
}