为什么不byte []来字符串和返回按预期工作 [英] why doesn't byte[] to string and back work as expected
问题描述
我有以下代码：
Int32 i1 = 14000000;
byte[] b = BitConverter.GetBytes(i1);
string s = System.Text.Encoding.UTF8.GetString(b);
byte[] b2 = System.Text.Encoding.UTF8.GetBytes(s);
Int32 i2 = BitConverter.ToInt32(b2,0);;
i2等于-272777233。
为什么不是输入值？ （14000000）？
i2 is equal to -272777233. Why isn't it the input value? (14000000) ?
编辑：我要执行的操作是将其附加到另一个字符串，然后使用WriteAllText将其写入文件
what I am trying to do is append it to another string which I'm then writing to file using WriteAllText
推荐答案
因为 Encoding 类不能满足任何需求。如果字符（在UTF-8中可能是几个字节）在该特定字符集中（在您的情况下是UTF-8）不是有效字符，它将使用替换字符。
Because an Encoding class is not going to just work for anything. If a "character" (possibly a few bytes in case of UTF-8) is not a valid character in that particular character set (in your case UTF-8), it will use a replacement character.
单个问号（U + 003F）
a single QUESTION MARK (U+003F)
（来源： http://msdn.microsoft.com/ zh-cn / library / ms404377.aspx＃FallbackStrategy ）
在某些情况下，它只是一个？，例如在ASCII / CP437 / ISO 8859-1中，但是您可以选择一种处理方式。 （请参见上面的链接）
Some case it is just a ?, for example in ASCII/CP437/ISO 8859-1, but there is a way for you to choose what to do with it. (See the link above)
例如，如果您尝试将（byte）128 转换为ASCII：
For example if you try to convert (byte)128 to ASCII:
string s = System.Text.Encoding.ASCII.GetString(new byte[] { 48, 128 }); // s = "0?"
然后将其转换回去：
byte[] b = System.Text.Encoding.ASCII.GetBytes(s); // b = new byte[] { 48, 63 }
您将不获取原始字节数组。
You will not get the original byte array.
这可以作为参考：检查字符是否在编码中
我无法想象为什么需要将字节数组转换为字符串。显然这没有任何意义。假设您要写入流，则可以直接写入 byte [] 。如果需要在某种文本表示形式中使用它，则只需将 yourIntegerVar.ToString（）转换为字符串并使用 int .TryParse 找回。
I can't imagine why you would need to convert a byte array to a string. It obviously doesn't make any sense. Let's say you're going to write to a stream, you could just directly write byte[]. If you need to use it in some text representation, it makes perfect sense to just convert it to a string by yourIntegerVar.ToString() and use int.TryParse to get it back.
编辑：
您可以将字节数组写入文件，但是您不会将字节数组连接为字符串并使用惰性方法 File.WriteAllText ，因为它将处理编码转换，您可能最终会遇到问号？全部在您的文件上。而是打开 FileStream 并使用 FileStream.Write 直接写入字节数组。或者，您可以使用 BinaryWriter 直接以其二进制形式（以及字符串）写入一个整数，并使用其对应的 BinaryReader 读回。
You can write a byte array to a file, but you are not going to "concatenate" the byte array to a string and use the lazy method File.WriteAllText because it is going to handle the encoding conversion and you will probably end up having question marks ? all over your file. Instead, Open a FileStream and use FileStream.Write to directly write the byte array. Alternatively, you can use a BinaryWriter to directly write an integer in its binary form (and also a string) and use its counterpart BinaryReader to read it back.
示例：
FileStream fs;
fs = File.OpenWrite(@"C:\blah.dat");
BinaryWriter bw = new BinaryWriter(fs, Encoding.UTF8);
bw.Write((int)12345678);
bw.Write("This is a string in UTF-8 :)"); // Note that the binaryWriter also prefix the string with its length...
bw.Close();
fs = File.OpenRead(@"C:\blah.dat");
BinaryReader br = new BinaryReader(fs, Encoding.UTF8);
int myInt = br.ReadInt32();
string blah = br.ReadString(); // ...so that it can read it back.
br.Close();
此示例代码将生成与以下十六进制转储匹配的文件：
This example code will result in a file which matches the following hexdump:
00 4e 61 bc 00 1c 54 68 69 73 20 69 73 20 61 20 73 Na¼..This is a s
10 74 72 69 6e 67 20 69 6e 20 55 54 46 2d 38 20 3a tring in UTF-8 :
20 29 )
请注意， BinaryWriter.Write（string） 还会在字符串前面加上长度，并且在回读时取决于字符串，因此不适合使用文本编辑器来编辑结果文件。 （那么您正在以二进制形式编写一个整数，因此我希望这是可以接受的吗？）
Note that BinaryWriter.Write(string) also prefix the string with its length and it depends on it when reading back, so it is not appropriate to use a text editor to edit the resulting file. (Well you are writing an integer in its binary form so I expect this is acceptable?)
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