CODEWITHSUNDEEP
cvisual-studiostreamllvm
YAKOVM
YAKOVM

Reputation: 10153

streams and llvm error

Here is the code of the functions: 

int getStream()
    {
           int fd = _dup(fileno(stdout));
           freopen("tmp","w",stdout);
           return fd;
    }


void freeStream(int fd)
{
       _dup2(fd,fileno(stdout));
       close(fd);
}

The code of main program:

printf(“start tets”);
int fd = getStream();
printf(“redirection”);
freeStream(fd);

This is a part of large program which uses llvm The problem I get after freeStream(fd): LLVM ERROR: IO failure on output stream. I understand that the problem is with freeStream implementation. What do you think? Thanks

Upvotes: 2

Views: 2517

Answers (2)

Jonathan Leffler
Jonathan Leffler

Reputation: 754110

As Jason diagnosed, you need to fflush() the stream (stdout) before you close the underlying file (via the _dup2() call).

Another problem is that there is no error checking in the code; you don't know which, if any, of your function calls are failing. At least while resolving this issue, you need to monitor both freopen() and _dup2() to ensure they work.

It is not clear that on Windows, you can reach behind the back of the <stdio.h> library and change the file descriptor. On Unix, I think it would likely work - not necessarily supported, but probably it would work. But I can easily imagine ways it fails on Windows (without being certain that my imagination is not simply being to vivid).

Ultimately, I am not convinced there's a portable way to reinstate stdout back to its original output after using freopen() on it.

Upvotes: 2

Jason
Jason

Reputation: 32520

If you want to reliably see the text "redirection" end up in your temporary file, you'll need to flush the buffer in stdout before you close it to get rid of any pending writes that are buffered in the stream. To accomplish this, add this line to your freeStream function:

void freeStream(int fd)
{
   fflush(stdout); //<== add this line
   _dup2(fd,fileno(stdout));
   close(fd);
}

Upvotes: 3

Related Questions