有没有办法存储无符号长的核心数据？ [英] Is there any way to store unsigned long in core data?

问题描述

CoreData提供了Integer 16，Integer 32和Integer 64存储，但不支持任何符号限定符。您可以将无符号整数（32位）存储为有符号长整型（64位），并确保该值保留全范围，但无符号长整形似乎需要一个128位有符号整数存储，当然，支持CoreData。有没有什么办法，然后存储unsigned long在coreData？

解决方案

[上一个评论晋升为回答]

听起来像是对你很重要的位模式，而不是整数值本身。你可以把它存储为一个有符号的 - 只是把它转换为C有符号< - >无符号转换不强制数学正确性，只保留位。

是在（Obj-）C（++）中，您可以将无符号整数值存储到具有等效有符号整数类型的变量中，反之亦然。 C转换从signed - > unsigned by定义等同于使用2的补码整数时的位复制，两种类型是相同的大小。换句话说，无符号 - >有符号，是实现定义 - 在实践中，通常 意思是位拷贝。 ang GCC使用一个位复制为两个，但如果你想绝对肯定可以使用联合：

  unsigned long r; 
 long l; 
 
 r =（unsigned long）l; //将永远工作（可选）
 
 //下面是l =（long）r（可选的）没有implementation defined的风险
 {union {long sValue; unsigned long uValue; } tmp; tmp.uValue = r; l = tmp.sValue;} 
  

但是我真的怀疑任何人会！ （注意：Clang至少会将其编译为直接赋值（位复制）。）

CoreData provides Integer 16, Integer 32 and Integer 64 storage, but doesn't support any sign qualifiers. You can store an unsigned int (32 bit) as a signed long (64 bit) and make sure the value is preserved for the full range, but an unsigned long seems to require a 128 bit signed integer to store, which of course isn't supported by CoreData. Is there any way then to store unsigned long in coreData?

解决方案

[Previous comment promoted to answer]

Sounds like it is the bit pattern which is important to you and not the integer value per se. You can store it as a signed - just cast it as C signed<->unsigned casts don't enforce mathematical correctness and just preserve the bits. Cast it back to use it.

Follow up question:

In general yes in (Obj-)C(++) you can store an unsigned integer value into a variable with the equivalent signed integer type, and vice-versa. C casts from signed -> unsigned by definition equate to a bit-copy when using 2's complement integers and the two types are the same size. Going the other way, unsigned -> signed, is "implementation defined" - which in practice usually means a bit-copy. Clang & GCC use a bit-copy for both, but if you want to be absolutely certain you can use a union:

unsigned long r;
long l;

r = (unsigned long)l; // will always work (cast optional)

// following is l = (long)r (cast optional) without "implementation defined" risk
{ union { long sValue; unsigned long uValue; } tmp; tmp.uValue = r; l = tmp.sValue;}

But seriously I doubt anybody would! (Note: Clang at least will compile it down to a straight assignment (bit-copy).)

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