Unix 线程改变创建进程中变量的值（2）

执行环境：Linux ubuntu 4.4.0-31-generic #50-Ubuntu SMP Wed Jul 13 00:07:12 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

1.测试代码： a.c

#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <pthread.h>
#include <string.h>

pthread_t ntid;

void * thr_fn(void * arg)
{
   int * fp = (int *)arg;
   char * str = (char *)arg; 

   printf("I am a thread,receive a string:%s",str);
   printf("Now,I will change it's value.
");
    
   strcpy(str,"Changed by a thread!
");
   return ((void *)0);
}

int main(void)
{
    int err;
    int fd;
    char parent[100] = "I am parent!
"; 

    fd = open("log.txt",O_CREAT|O_WRONLY);
    if(-1 == fd)
    {
    printf("Failed to open  file!
");
    }

    err = pthread_create(&ntid,NULL,thr_fn,parent);
    if(err != 0)
    {
    printf("can't create thread ,errno = %d
",err);    
    }

    void ** pr;
    err = pthread_join(ntid,pr);
    if(err !=0 )
    {
       printf("error happend when waited a thread!
");
    }
    printf("In process,the value of the string is %s",parent);
    return 0;
}

2.输出：

I am a thread,receive a string:I am parent!
Now,I will change it's value.
In process,the value of the string is Changed by a thread!

3.创建进程是通过指针传递参数给线程的，线程又是共享创建进程的一些资源的，可以改变进程的变量值。

  php 在创建线程的时候，线程对象需要保存进程传递进来参数的值的方式是传值，如果在构造函数中，引用传递进来的参数，会报错误：

  Fatal error: Cannot assign by reference to overloaded object。