How to increase the limit of “maximum open files” in C on Mac OS X

Question

The default limit for the max open files on Mac OS X is 256 (ulimit -n) and my application needs about 400 file handlers.

I tried to change the limit with setrlimit(

Answer 1

This may be a hard limitation of your libc. Some versions of solaris have a similar limitation because they store the fd as an unsigned char in the FILE struct. If this is the case for your libc as well, you may not be able to do what you want.

As far as I know, things like setrlimit only effect how many file you can open with open (fopen is almost certainly implemented in terms on open). So if this limitation is on the libc level, you will need an alternate solution.

Of course you could always not use fopen and instead use the open system call available on just about every variant of unix.

The downside is that you have to use write and read instead of fwrite and fread, which don't do things like buffering (that's all done in your libc, not by the OS itself). So it could end up be a performance bottleneck.

Can you describe the scenario that requires 400 files open ** simultaneously**? I am not saying that there is no case where that is needed. But, if you describe your use case more clearly, then perhaps we can recommend a better solution.