Tutorial :What is a good way to recover from a fread() failure?


If a call to fread() returns 0 and ferror() indicates an error (vs. EOF), is it OK to retry the read or is it better to close and reopen the file?

I can't start over entirely -- the input file has been partially processed in a way that can't be undone (say I'm writing out a chunk at a time to a socket and, due to existing protocol, have no way of telling the remote end, "never mind, I need to start over").

I could fclose() and fopen() the file, fseek() past the data already processed, and continue the fread()-ing from there, but is all that necessary?


There's no "one size fits all" solution, since different errors can require different handling. Errors from fread() are unusual; if you're calling it correctly, an error may indicate a situation that has left the FILE* in a weird error state. In that case you're best off calling fclose(), fopen(), fseek() to get things back in a good state.

If you're coding for something that's happening, please mention the actual errors you're getting from ferror()...


You can give the clearerr function a look.


You can show the error to the user with perror() or strerror() and ask her is she wants to retry.

It's not mandatory for the implementation to provide such an error message, though. You should set errno to 0 before calling fread(); if it fails and errno is still 0 then no error information will be available.

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