1 #include <fcntl.h>
 2 #include <unistd.h>
 3 #include <stdio.h>
 4 #include <pthread.h>
 5 #include <string.h>
 6 
 7 pthread_t ntid;
 8 
 9 void * thr_fn(void * arg)
10 {
11    int * fp = (int *)arg;
12    char * str = (char *)arg; 
13 
14    printf("I am a thread,receive a string:%s",str);
15    printf("Now,I will change it‘s value.\n");
16     
17    strcpy(str,"Changed by a thread!\n");
18    return ((void *)0);
19 }
20 
21 int main(void)
22 {
23     int err;
24     int fd;
25     char parent[100] = "I am parent!\n"; 
26 
27     fd = open("log.txt",O_CREAT|O_WRONLY);
28     if(-1 == fd)
29     {
30     printf("Failed to open  file!\n");
31     }
32 
33     err = pthread_create(&ntid,NULL,thr_fn,parent);
34     if(err != 0)
35     {
36     printf("can‘t create thread ,errno = %d\n",err);    
37     }
38 
39     void ** pr;
40     err = pthread_join(ntid,pr);
41     if(err !=0 )
42     {
43        printf("error happend when waited a thread!\n");
44     }
45     printf("In process,the value of the string is %s",parent);
46     return 0;
47 }

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!