RE: fread/fwrite/fflush bug

Someone pointed out the fpurge() function.  Calling fpurge() on the reader before the 2^nd read fixes the problem.

 

Norm Green

 

 

 

I’ve found what I consider to be a stream IO bug.  The code below can be compiled with g++ to easily illustrate the problem. Here’s what’s happening:

 

1. Open a file for writing (using fopen(…, “w”) ) and write some data to the file
2. Flush the writer using fflush()
3. Open a second stream to the file for reading only using fopen(…., “r”)
4. Read some bytes using fseek() & fread() to confirm the reader can see the data written in step 1
5. Have the writer update 1 byte using fwrite()
6. Flush the writer using fflush()
7. Using the read stream, read the byte written by the writer in step 5 using fseek() / fread()
8. You will get the wrong answer here.  The read should return the byte written in step 5 but instead returns the old value written in step 1.

 

Is this is a bug in Darwin?  Are there any work arounds? 

 

Here’s my test case code.  BTW, it passes on Solaris.

 

Norm Green