line_391--2009-4-14 16:38:09

  由 391 至 404 , 通过duplicate 一个stdout的descriptor来判读stdout是否有效.
代码如下:

main的代码

//clien/mysql.cc 
int main(int argc,char *argv[])
{
  char buff[80];

  MY_INIT(argv[0]); // 初始话化THR_KEY_mysys指向的线程环境,并初始化一些互斥量和锁.
  DBUG_ENTER("main");
  DBUG_PROCESS(argv[0]);
#pragma  region SET_TERMINAL //设置交互终端的状态.
  delimiter_str= delimiter; 
  default_prompt = my_strdup(getenv("MYSQL_PS1") ? 
        getenv("MYSQL_PS1") : 
        "mysql> ",MYF(MY_WME)); 
  current_prompt = my_strdup(default_prompt,MYF(MY_WME)); 
  prompt_counter=0;

  outfile[0]=0;   // no (default) outfile
  strmov(pager, "stdout"); // the default, if --pager wasn't given
  {
    char *tmp=getenv("PAGER");
    if (tmp && strlen(tmp))
    {
      default_pager_set= 1;
      strmov(default_pager, tmp);
    }
  }
  if (!isatty(0) || !isatty(1))
  {
    status.batch=1; opt_silent=1;
    ignore_errors=0;
  }
  else
    status.add_to_history=1;
  status.exit_status=1;
#pragma endregion SET_TERMINAL
  { #pragma region PROMOTE_STDOUT //保证stdout有效,且可以访问.
    /* 
     The file descriptor-layer may be out-of-sync with the file-number layer,
     so we make sure that "stdout" is really open.  If its file is closed then
     explicitly close the FD layer. 
    */
    int stdout_fileno_copy;
    stdout_fileno_copy= dup(fileno(stdout)); /* Okay if fileno fails. */
    if (stdout_fileno_copy == -1)
      fclose(stdout);
    else
      close(stdout_fileno_copy);             /* Clean up dup(). */
  }
#pragma endregion PROMOTE_STDOUT
  ...
}