I have a problem using Apache Portable Runtime on Ubuntu with GCC 4.8.1
The problem is that the off64_t from <sys/types.h> is not available when compiling with gcc. (When compiling with g++ everything work fine)
Does anybody know which compiler switch to use to enable off64_t? (I know that defining _LARGEFILE_SOURCE _LARGEFILE64_SOURCE avoids the problem, but wondering if this is the right way)
To reproduce the error one can simply try to compile the following code:
#include <sys/types.h>
off64_t a_variable;
Answer
off64_t is not a language defined type. No compiler switch will make it available.
It is defined in sys/types.h, but (on a 32 bit system) only if
_LARGEFILE64_SOURCE is defined
Which will make the 64 bit interfaces available (off64_t, lseek64(), etc...).
The 32 bit interfaces will still be available by their original names._FILE_OFFSET_BITS is defined as '64'
Which will make the names of the (otherwise 32 bit) functions and data types refer to their 64 bit counterparts.
off_t will be off64_t, lseek() will use lseek64(), and so on...
The 32 bit interface is no longer available.
Make sure that if you define these macros anywhere in your program, you define them at the beginning of all your source files. You don't want ODR violations to be biting you in the ass.
Note, this is for a 32 bit system, where off_t is normally a 32 bit value.
On a 64 bit system, the interface is already 64 bits wide, you don't need to use these macros to get the large file support.
off_t is a 64 bit type, lseek() expects a 64 bit offset, and so on.
Additionally, the types and functions with 64 in their name aren't defined, there's no point.
See http://linux.die.net/man/7/feature_test_macros
and http://en.wikipedia.org/wiki/Large_file_support
You also may be interested to know that when using g++, _GNU_SOURCE is automatically defined, which (with the gnu c runtime library) leads to _LARGEFILE64_SOURCE being defiend. That is why compiling your test program with g++ makes off64_t visible. I assume APR uses the same logic in making _LARGEFILE64_SOURCE defined.