Question

我有一个TCP代码，但它一直在服务器代码中给我错误。

当我使用valgrind运行它时，我在服务器终端中获得以下内容：

    ==12370== Use of uninitialised value of size 8
==12370==    at 0x4E6B506: ____strtol_l_internal (in /lib64/libc-2.18.so)
==12370==    by 0x4E687DF: atoi (in /lib64/libc-2.18.so)
==12370==    by 0x400F1D: main (in /mnt/castor/seas_home/x/xyz/TCP/serv)
==12370== 
==12370== Invalid read of size 1
==12370==    at 0x4E6B506: ____strtol_l_internal (in /lib64/libc-2.18.so)
==12370==    by 0x4E687DF: atoi (in /lib64/libc-2.18.so)
==12370==    by 0x400F1D: main (in /mnt/castor/seas_home/a/xyz/TCP/serv)
==12370==  Address 0xffdfffac00000 is not stack'd, malloc'd or (recently) free'd
==12370== 
==12370== 
==12370== Process terminating with default action of signal 11 (SIGSEGV)
==12370==  General Protection Fault
==12370==    at 0x4E6B506: ____strtol_l_internal (in /lib64/libc-2.18.so)
==12370==    by 0x4E687DF: atoi (in /lib64/libc-2.18.so)
==12370==    by 0x400F1D: main (in /mnt/castor/seas_home/a/xyz/TCP/serv)
==12370== 
==12370== HEAP SUMMARY:
==12370==     in use at exit: 0 bytes in 0 blocks
==12370==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==12370== 
==12370== All heap blocks were freed -- no leaks are possible
==12370== 
==12370== For counts of detected and suppressed errors, rerun with: -v
==12370== Use --track-origins=yes to see where uninitialised values come from
==12370== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 2 from 2)

但我无法弄清楚如何解决它。有谁能告诉我如何解决这个问题？

Answer 1

这是您的代码的重要部分：

char *words[10];
char buffer[1024];
memset(buffer, 0, sizeof buffer);
nwords = getwords(buffer, words, 10);
option = atoi(words[0]);

因为您使用空缓冲区调用getwords，它将返回0并且未在words中设置任何内容，因此words[0]也未初始化。您没有检查getwords的返回值，但您应该这样做。如果nwords==0，则不应使用words[0]。

Answer 2

there are several basic problems with the server code.
here is just one that needs correction.

the server code is using the 'listen'/'accept' socket 
to write to the client.  
However, the accept function returns a NEW socket
That new socket is the one to use to communicate with the client.

here is an excerpt from the man page about the accept() function.

   The  accept()  system  call  is used with connection-based socket types
   (SOCK_STREAM,  SOCK_SEQPACKET).   It  extracts  the  first   connection
   request  on  the queue of pending connections for the listening socket,
   sockfd, creates a new connected socket, and returns a new file descrip‐
   tor  referring  to that socket.  The newly created socket is not in the
   listening state.  The original socket  sockfd  is  unaffected  by  this
   call.

   The  argument  sockfd is a socket that has been created with socket(2),
   bound to a local address with bind(2), and is listening for connections
   after a listen(2).

关键信息是：

"creates a new connected socket, and returns a new file descrip‐
   tor  referring  to that socket."

suggest reading the manual 
for system functions that are called within your code

所以变量＆＃39; recsize＆＃39;实际上是一个与客户端进行通信的套接字。

在TCP代码中获取未初始化的值错误

2 个答案: