Macros (C/C++) for reading/writing file on different architectures/ C compiler

The following header file is extracted from my project that requires writing and reading large blocks of data from hard-disks. One of requirements is the code should be portable in common operating systems and compatible to common compilers.

#ifndef _SLAS_PORTABLE_
#define _SLAS_PORTABLE_
 
// Windows
#if defined(_WIN32) || defined(_WIN64)
    #if _MSC_VER == 1200 // VC++ 6.0
            #define spos_t long
                #define sftell(stream) ftell(stream)
                #define sfseek(stream, offset, origin)  fseek(stream, offset, origin)
    #endif
    #if _MSC_VER > 1200  // from VC++ 7.0 above
        #define spos_t __int64
 
        #ifndef _FSEEKI64_VC
            #define  _FSEEKI64_VC
            extern "C" int __cdecl _fseeki64(FILE *, __int64, int)
            extern "C" __int64 __cdecl _ftelli64(FILE *)
        #endif
 
        #define sftell(stream) _ftelli64(stream)
        #define sfseek(stream, offset, origin)  _fseeki64(stream, offset, origin)
    #endif
#endif
 
// Unix or Linux
#if defined(__unix_) || defined(__linux__)
    #if _INTEGRAL_MAX_BITS >= 64 // 64 bit machine
        #define _FILE_OFFSET_BITS 64 // this will turn off_t into 64-bit type
        #endif
 
    #define spos_t off_t
        #define sftell(stream) ftello(stream)
        #define sfseek(stream, offset, origin)  fseeko(stream, offset, origin)
#endif
 
// Mac OSX
#ifdef __APPLE__
    #if _INTEGRAL_MAX_BITS >= 64 // 64 bit machine
          #define _FILE_OFFSET_BITS 64 // this will turn off_t into 64-bit type
    #endif                                                                      
 
    #define spos_t off_t
    #define sftell(stream) ftello(stream)
    #define sfseek(stream, offset, origin)  fseeko(stream, offset, origin)
#endif
 
#endif
 
/*Problem with fseek on opened text stream
 
  Read this http://msdn.microsoft.com/en-us/library/75yw9bf3.aspx
*/