Thread: O_largefile ???

When trying to compile a fairly large program, I get the following:

Code:

adios_posix1.c:89: error: ‘O_LARGEFILE’ undeclared (first use in this function)
adios_posix1.c:89: error: (Each undeclared identifier is reported only once
adios_posix1.c:89: error: for each function it appears in.)

Any suggestions? I need to change something in the Makefile, which is also fairly large.

This is what I'm trying to build:
National Center for Computational Sciences » ADIOS
1.2.1

I honestly can only find unhelpful information via google.

Originally Posted by Ronix

I believe O_LARGEFILE is a GNU extension. Add `_GNU_SOURCE' to the defined preprocessor symbols and see if it works.

I'm quite new to C. I don't know how to add to defined preprocessor symbols, or what those are.

Sorry for my ignorance.

Am I asking incorrectly, or is it something that's not so easy?

Originally Posted by cas

First off, O_LARGEFILE is indeed a GNU extension. If you're not on a system with glibc (which basically means if you're not on Linux), simply get rid of O_LARGEFILE (or read your system's documentation on large file support).

If you are on Linux, the open(2) man page should tell you about O_LARGEFILE: “(LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened. The _LARGEFILE64_SOURCE macro must be defined in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of obtaining method of accessing large files on 32-bit systems (see feature_test_macros(7)).”

The good news is that on Linux, at least, you can magically figure out what you need for large file support via getconf. That is, you don't need to (and probably shouldn't) set _FILE_OFFSET_BITS by hand. On 64-bit systems, I suspect off_t is already 64-bit (but don't quote me, I'm still in 32-bit land). getconf will know what, precisely, is needed on each system. So:

Code:

getconf LFS_CFLAGS
getconf LFS_LDFLAGS
getconf LFS_LIBS

will tell you all you need to know about LFS on your system. Once you use the proper defines to get 64-bit file I/O, you should drop the O_LARGEFILE. It's not needed, and, as the man page hints at, obsolescent.

UPDATE: I suppose O_LARGEFILE is a Linux extension, not GNU. The rest of the post stands, though.

I see. I'm on a Mac, so I guess I will have to figure out where O_LARGEFILE is present and remove it.


Thank you very much for your help. It's MY fault for not specifying I'm on a Mac.

I removed the O_LARGEFILE in the opens and it now compiles.

Brilliant.