_ _int64 64位整数

超、凢脫俗 2023-06-27 11:09 6阅读 0赞

【MSVC】[http://msdn.microsoft.com/en-us/library/aa261215(v=vs.60).aspx][http_msdn.microsoft.com_en-us_library_aa261215_v_vs.60_.aspx]

允许使用64位的整数

使用之前先判断是否支持64位整数

_#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][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**, and**long** 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 **\_ \_int***x*. 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

[http_msdn.microsoft.com_en-us_library_aa261215_v_vs.60_.aspx]: http://msdn.microsoft.com/en-us/library/aa261215%28v=vs.60%29.aspx
[http_bytes.com_topic_c_answers_214990-defining-int64]: http://bytes.com/topic/c/answers/214990-defining-int64