折腾了半天的动态内存与多线程

本想试验一下，动态分配的内存内容在传给另一个线程后，如何显示。

背景是tcmd,free()后出段错误，我就自己写了一个小程序，试验一下。

代码如下：

#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
typedef struct {
char buff[30];
void *data;
}OP_TCMD;
void* thread1(char *buff1)
{
  int i;
  char buff[30];
  memset(buff, 0, 30);
  memcpy(buff, buff1,strlen(buff1));
  printf("begin buff: %s ,len = %d \n",buff, strlen(buff));
  for(i=0; i<10;i++)
  {
    printf("buff[%d]= %d\n", i, buff[i]);
  }
   printf("end\n");
}
void* thread2(OP_TCMD *tcmd)
{
  int i;
  char buff[30];
  memcpy(buff, tcmd->data, 30);
  printf("buff:%s\n", buff);
  printf("data addr:%08x \n ", &tcmd->data);

  //printf("begin, %d %s \n",strlen(tcmd->data), tcmd->data);

  for(i=0; i<10;i++)
  {
    printf("buff[%d]= %04x\n", i, buff[i]);
   }
   
   printf("end\n");
}
int main()
{
   OP_TCMD *tcmd;
   OP_TCMD tcmd_get;
   tcmd =&tcmd_get;
   pthread_t thread_id;
   int state;
  
  
   char *buff="hello world , icommonweal";
   char *dynamic= (char *)malloc(30);
   memset(dynamic, 0, 30);
   strncpy(dynamic, buff, strlen(buff));
   
   memset(tcmd_get.buff, 0, 30);
   strncpy(tcmd_get.buff, "1234", 4);
  
   printf("dynamic buff: %s len= %d\n",dynamic, strlen(dynamic));
   tcmd_get.data = dynamic ;
   printf("dynamic:%08x \n ", &dynamic);

   /*create thread */
   state=pthread_create(&thread_id, NULL,(void *)&thread1 ,(void*)dynamic);
   if(state<0)
   {
       printf("create thread failed\n");
   }
   else
   {
        // pthread_detach(thread_id);

         printf("create thread sucess\n");
   }
   
  free(dynamic);
   pthread_join(thread_id, NULL);
  
   return 0;
}

   在state=pthread_create(&thread_id, NULL,(void *)&thread1 ,(void*)dynamic);

   后，本想看到它会把动态分配内存中的东西打印出来，却显示

dynamic buff: hello world , icommonweal len= 25
dynamic:bfa858a0
 create thread sucess
begin buff: ,len = 0
buff[0]= 0
buff[1]= 0
buff[2]= 0
buff[3]= 0
buff[4]= 0
buff[5]= 0
buff[6]= 0
buff[7]= 0
buff[8]= 0
buff[9]= 0
end



怎么是len=0，我想不懂，难道动态内存分配的东西传入不到线程中去??

我也写了另一个线程thread2，把数据指针放入到tcmd_get.data = dynamic ; state=pthread_create(&thread_id, NULL,(void *)&thread2 ,(void*)tcmd);

执行显示也是

root@:/home/qing/lib# ./a.out
dynamic buff: hello world , icommonweal len= 25
dynamic:bfd73380
 create thread sucess
buff:
data addr:bfd733b0
 buff[0]= 0000
buff[1]= 0000
buff[2]= 0000
buff[3]= 0000
buff[4]= 006f
buff[5]= 0020
buff[6]= 0077
buff[7]= 006f
buff[8]= 0072
buff[9]= 006c
end



buff为空， buff[0]= 0000
buff[1]= 0000
buff[2]= 0000
buff[3]= 0000

真是奇怪了，怎么想也不明白，但只要是把

  tcmd_get.data = dynamic ;改为tcmd_get.data = buff;

state=pthread_create(&thread_id, NULL,(void *)&thread2 ,(void*)tcmd);就能正确显示：

root@:/home/qing/lib# ./a.out
dynamic buff: hello world , icommonweal len= 25
dynamic:bfac78e0
 create thread sucess
buff:hello world , icommonweal
data addr:bfac7910
 buff[0]= 0068
buff[1]= 0065
buff[2]= 006c
buff[3]= 006c
buff[4]= 006f
buff[5]= 0020
buff[6]= 0077
buff[7]= 006f
buff[8]= 0072
buff[9]= 006c
end



能正确的显示。

同样，把 state=pthread_create(&thread_id, NULL,(void *)&thread1 ,(void*)dynamic);

改为 state=pthread_create(&thread_id, NULL,(void *)&thread1 ,(void*)buff);

也能正确显示：

root@:/home/qing/lib# ./a.out
dynamic buff: hello world , icommonweal len= 25
dynamic:bf816630
 create thread sucess
begin buff: hello world , icommonweal ,len = 25
buff[0]= 104
buff[1]= 101
buff[2]= 108
buff[3]= 108
buff[4]= 111
buff[5]= 32
buff[6]= 119
buff[7]= 111
buff[8]= 114
buff[9]= 108
end



难道真是线程不能处理动态内存的内容？、

最终发现错误的地方：

free(dynamic);
pthread_join(thread_id, NULL);
  

在主线程free()后，开启的线程当然不后显示正确。如果两句倒一下位置就可以正确显示了。

 
pthread_join(thread_id,NULL);
  

free(dynamic);