_ _int 64 비트 정수

_#if defined (_INTEGRAL_MAX_BITS) && \
  _INTEGRAL_MAX_BITS >= 64
typedef signed __int64 int64;
typedef unsigned __int64 uint64;
#else
#error __int64 type not supported
#endif
  【GGC】 
http://bytes.com/topic/c/answers/214990-defining-int64 
I use this in my code

#if defined(_MSC_VER) || defined(__BORLANDC__)
typedef unsigned __int64 ulong64;
typedef signed __int64 long64;
#else
typedef unsigned long long ulong64;
typedef signed long long long64;
#endif

It works for GCC, MSVC and BorlandC which will cover the vast majority of
platforms.
  
The _ _int64 keyword declares a new type, a 64-bit (8-byte) integer. As with the int, short, andlong types, the _ _int64 type has a corresponding unsigned version, so the _ _int64 keyword actually can be used to create two types. 
The following code sample shows how to declare two 64-bit integers, one signed and the other unsigned: 
__int64            signed_big_int;
unsigned __int64   unsigned_big_int;
  
In the printf family of run-time library functions, the format for optional prefixes includes I64, in addition to F, N, h, l, and L. For example, the following statement includes an example of a valid format string: 
printf("%I64d", x);
  
When manipulating 64-bit integers, no special functions are necessary. Ordinary arithmetic operators and operations behave as expected. 
Note   Both the Alpha edition and the x86 edition of Visual C++ support the _ _int64 data type. However, the support in the Alpha edition is more complete; in particular, the integrated debugger recognizes _ _int64 variables in the Alpha edition but not in the x86 edition. Also, both editions provide full support for the _ _int8, _ _int16, and _ _int32 types. Use of these types is not recommended, except in situations where the program must interact with a fixed-byte layout (for example, in reading records previously stored on disk). 
Use of _ _int64 should be conditional on the predefined macro _INTEGRAL_MAX_BITS. This macro describes the maximum size of integers defined using the form _ _intx. For example: 
_#if defined (_INTEGRAL_MAX_BITS) && \
  _INTEGRAL_MAX_BITS >= 64
typedef signed __int64 int64;
typedef unsigned __int64 uint64;
#else
#error __int64 type not supported
#endif