线程默认共享数据段、代码段等地址空间，常用的是全局变量。而进程不共享全局变量，只能借助mmap。

//代码示例

#include <string.h>
#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>int var = 100;void *tfn(void *arg)
{var = 200;printf("In thread, the var is %d.\n",var);return NULL;
}int main(void)
{pthread_t tid;int ret;printf("In main, the var is %d at first.\n",var);ret = pthread_create(&tid, NULL, tfn, NULL);if( ret != 0 )   //出错判断{fprintf(stderr,"pthread_create error: %s\n",strerror(ret));exit(1);}sleep(1);printf("In main, the var is %d after thread's ending.\n",var);return 0;
}

[root@localhost 01_pthread_test]# ./pthrd_crt

In main, the var is 100 at first.

In thread, the var is 200.

In main, the var is 200 after thread's ending.