c - 接收和打印

Question

为了确定...下面的代码是否应该准确打印服务器发送的内容？我收到一些不需要的模式，例如 ^M5b3^M 、 ^M800^M 等。IE。而不是这个:

 <P k="33,556,1" v="-0.166723"/>

我得到了这个:

<P k="33,556,1" v="-0.16672^M
2000^M
3"/>

这段代码有问题吗？或者数据是否已损坏？

 char * input_buffer = malloc(MAXLENGTH);

 for (;;) {

    bytes_received = recv ( socket_handle , input_buffer , MAXLENGTH, 0 ) ;
    *( input_buffer+bytes_received + 1 ) = '\0';
    if ( bytes_received == -1 ) {
      printf ( "An error occured during the receive procedure \n" ) ;
      return 0 ;
    }
    if ( bytes_received == 0 )continue ;
    printf ("%s", input_buffer);
  }

Answer 1

如果已读取 MAXLENGTH 字节，则此行

*( input_buffer+bytes_received + 1 ) = '\0';

写入超出分配的内存，这会引发未定义的行为。

它还将接收到的最后一个字符的 0 终止符写入 2 个字节。

1 要修复前者，请修改此行

char * input_buffer = malloc(MAXLENGTH);

成为

char * input_buffer = malloc(MAXLENGTH+1);

或修改此行

bytes_received = recv ( socket_handle , input_buffer , MAXLENGTH, 0 ) ;

成为

bytes_received = recv ( socket_handle , input_buffer , MAXLENGTH-1, 0 ) ;

2 要修复后者，请修改

 *( input_buffer+bytes_received + 1 ) = '\0';

成为

*(input_buffer+bytes_received) = '\0';

<小时/>

还有这一行

if ( bytes_received == 0 )continue ;

没有意义。如果 recv() 返回 0，则连接已关闭。通过此套接字描述符不再需要任何数据。

<小时/>

总而言之，代码看起来更好:

char * input_buffer = malloc(MAXLENGTH+1);
/* Add error checking here. */
for (;;) {

  ssize_t bytes_received = recv ( socket_handle , input_buffer , MAXLENGTH, 0 ) ;
  if ( bytes_received == -1 ) {
    printf ( "An error occured during the receive procedure \n" ) ;
    return 0 ;
  }

  *(input_buffer+bytes_received) = '\0';

  if ( bytes_received == 0 )
    return 0;

  printf ("%s", input_buffer);
}