string.GetHashCode（）在debug vs release中返回不同的值，如何避免这种情况？ [英] string.GetHashCode() returns different values in debug vs release, how do I avoid this?

问题描述

令我惊讶的是，在调试vs版本中，下面的方法产生了不同的结果：

  int result =test.GetHashCode （）; 
  

有什么办法可以避免吗？

我需要一个可靠的方法来排序字符串，我需要该值在调试和释放模式下保持一致。我想避免编写自己的散列函数，如果可能的话。

为什么会这样？

反馈给我：

  [ReliabilityContract（Consistency.WillNotCorruptState，Cer.MayFail），SecuritySafeCritical] 
 public override unsafe int GetHashCode（）
 {
 fixed（char * str =（（char *）this））
 {
 char * chPtr = str; 
 int num = 0x15051505; 
 int num2 = num; 
 int * numPtr =（int *）chPtr; 
（int i = this.Length; i> 0; i  -  = 4）
 {
 num =（（（num（<< 5）+ num） >> 0x1b））^ numPtr [0]; 
 if（i< = 2）
 {
 break; 
} 
 num2 =（（（num2 <5）+ num2）+（num2>> 0x1b））^ numPtr [1] 
 numPtr + = 2; 
} 
 return（num +（num2 * 0x5d588b65））; 
} 
} 
  

解决方案

code> GetHashCode（）是不是几乎100％的时间你应该用来哈希字符串。不知道你在做什么，我建议你使用一个实际的哈希算法，如SHA-1：

  using .Security.Cryptography.SHA1Managed hp = new System.Security.Cryptography.SHA1Managed（））{
 //使用hp.ComputeHash（System.Text.Encoding.ASCII（或Unicode，UTF8，UTF16或UTF32或某些东西...）GetBytes（theString）来计算哈希码
} 
  

更新对于某些东西要快一些，还有 SHA1Cng ，明显快于 SHA1Managed 。

To my surprise the folowing method produces a different result in debug vs release:

int result = "test".GetHashCode();

Is there any way to avoid this?

I need a reliable way to hash a string and I need the value to be consistent in debug and release mode. I would like to avoid writing my own hashing function if possible.

Why does this happen?

FYI, reflector gives me:

[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail), SecuritySafeCritical]
public override unsafe int GetHashCode()
{
    fixed (char* str = ((char*) this))
    {
        char* chPtr = str;
        int num = 0x15051505;
        int num2 = num;
        int* numPtr = (int*) chPtr;
        for (int i = this.Length; i > 0; i -= 4)
        {
            num = (((num << 5) + num) + (num >> 0x1b)) ^ numPtr[0];
            if (i <= 2)
            {
                break;
            }
            num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ numPtr[1];
            numPtr += 2;
        }
        return (num + (num2 * 0x5d588b65));
    }
}

解决方案

GetHashCode() is not what you should be using to hash a string, almost 100% of the time. Without knowing what you're doing, I recommend that you use an actual hash algorithm, like SHA-1:

using(System.Security.Cryptography.SHA1Managed hp = new System.Security.Cryptography.SHA1Managed()) {
    // Use hp.ComputeHash(System.Text.Encoding.ASCII (or Unicode, UTF8, UTF16, or UTF32 or something...).GetBytes(theString) to compute the hash code.
}

Update: For something a little bit faster, there's also SHA1Cng, which is significantly faster than SHA1Managed.

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