How to enable large file support under Darwin?

Question

I have a C application I am trying to compile for Mac OS X 10.6.4:

$ uname -v
Darwin Kernel Version 10.4.0: Fri Apr 23 18:28:53 PDT 2010; root:xnu-1504.7.4~1/RELEASE_I386

My gcc is as follows:

$ gcc --version
i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5664)

My Makefile is as follows:

CC=gcc
CFLAGS=-D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE -O3 -Wformat -Wall -pedantic -std=gnu99

all: myApp
    rm -rf *~

myApp: myApp.o
    ${CC} ${CFLAGS} myApp.o -lbz2 -o myApp
    rm -rf *~

clean:
    rm -rf *.o myApp

The issue is that my application makes calls to fseeko64 and fopen64, and uses the off64_t type for offsets. When I compile my application I get the following warnings and errors:

$ make myApp
gcc -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE -O3 -Wformat -Wall -pedantic -std=gnu99   -c -o myApp.o myApp.c
myApp.c: In function ‘extractData’:
myApp.c:119: warning: implicit declaration of function ‘fseeko64’
myApp.c:119: error: ‘off64_t’ undeclared (first use in this function)
myApp.c:119: error: (Each undeclared identifier is reported only once
myApp.c:119: error: for each function it appears in.)
myApp.c: In function ‘extractMetadata’:
myApp.c:305: warning: implicit declaration of function ‘fopen64’
myApp.c:305: warning: assignment makes pointer from integer without a cast

My code builds without errors under Linux. What changes can I make to the source code to add large file support when building under Darwin?

Eward

Answer 1

On Darwin file I/O is 64-bit by default (10.5 at least), just found this by grepping in /usr/include:

sys/_types.h:typedef __int64_t  __darwin_off_t;

unistd.h:typedef __darwin_off_t     off_t;

So all you need to do is something like

#ifdef __APPLE__
#  define off64_t off_t
#  define fopen64 fopen
...
#endif

Merell

@AlexReynolds I wouldn't call it perfect, see my answer. – Youlandayoulton

Answer 2

While this question has an up-voted accepted answer which works I think the solution is a bit misleading. Instead of fixing something it's always better to avoid having to fix it later in the first place.

For example for the fopen64 function the GNU C Library docs say:

If the sources are compiled with _FILE_OFFSET_BITS == 64 on a 32 bits machine this function is available under the name fopen and so transparently replaces the old interface.

You can just use the same function fopen on systems that support 64-bit I/O by default and you can set the _FILE_OFFSET_BITS=64 flag on 32-bit without the need write redefines at all. The same goes for types like off64_t vs. off_t.

Save the redefines for the case when you have to deal with 3rd party sources and use standard functions in your own code.

Youlandayoulton

This should be the accepted answer. This is the right way to fix this. – Negrete

I looked into this more and although this should be the accepted answer for non-Darwin platforms, on Darwin they have made the file functions 64-bit, and _FILE_OFFSET_BITS and _LARGEFILE64_SOURCE don't exist. So the accepted answer is probably the best way to fix such a portability issue. – Negrete

Answer 3

The fseeko and similar commands work with large file support so no need for the fseeko64 etc Apple man page

Scotism