13.环境变量

1.设置环境变量

#include <stdlib.h>
extern char **environ;
int main(void){
    //获取环境变量caption的值
    char *p=getenv("caption");
    if(p==NULL)
        printf("not found...\n");
    else
        printf("caption=%s\n",p);
    
    setenv("caption","nanjing",1);
    p=getenv("caption");
    if(p==NULL)
        printf("setenv not found...\n");
    else
        printf("setenv caption=%s\n",p);
    //删除环境变量
    unsetenv("caption");
    p=getenv("caption");
    if(p==NULL)
        printf("unsetenv not found...\n");
    else
        printf("unsetenv caption=%s\n",p);
    clearenv();
    if(environ==NULL)
        printf("clear all...\n");
    return 0;
}

2.putenv

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

int main(void){
    char buf[128] = "location=shanghai";
    putenv(buf);
    char *p = getenv("location");
    if(p == NULL){
        printf("Can't find...\n");
    }
    else{
        printf("%s\n", p);
    }

    strcpy(buf, "location=beijing");
    p = getenv("location");
    if(p == NULL){
        printf("Can't find\n");
    }
    else
    {
        printf("new value: %s\n", p);
    }
    return 0;
 
}