将未知编码的TXT文件转换为字符串 [英] Convert TXT File of Unknown Encoding to String

问题描述

如果编码类型未知，我如何将纯文本（.txt）文件转换为字符串？

How can I convert Plain Text (.txt) files to a string if the encoding type is unknown?

我正在开发一个允许用户将txt文件导入我的应用程序。这意味着文件可能已经在任何数量的应用程序中创建，使用任何可被认为对纯文本文件有效的编码。我的理解是可以包括（ASCII，UTF-8，UTF-16，UTF-16BE，UTF-16LE，UTF-32，UTF-32BE，UTF-32LE或EBCDIC？！）

I'm working on a feature that would allow users to import txt files into my app. This means the file could have been created in any number of apps, utilizing any of a variety of encodings that would be considered valid for a plain text file. My understanding is this could include (ASCII, UTF-8, UTF-16, UTF-16BE, UTF-16LE, UTF-32, UTF-32BE, UTF-32LE, or EBCDIC?!)

使用以下内容，事情进展顺利：

Things had been going well using the following:

NSString *txtFileAsString = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:&errorReading];

然后，用户提供导入时导致空的内容的文件。我在XCode调试中看过该文件，看到Cocoa错误261，NSStringEncoding = 4。

Then a user supplied a file that resulted in empty content when imported. I watched the file in XCode debug, and see a Cocoa error 261, NSStringEncoding=4.

我知道：

• 用户提供的文件是使用名为knowtes的应用程序创建的。


• 该文件在Mac OS X上使用TextEdit，TextWranger等打开


• 该文件包含特殊字符，如umlauts（rant：为什么umlaut上的u不具有umlaut？！）


• Finder信息显示：

• The user supplied file was created with an app called knowtes
• The file opens with TextEdit, TextWranger, etc. on Mac OS X
• The file contains "special characters" such as umlauts (rant: why doesn't the "u" on umlaut have an umlaut?!)
• Finder Info displays:

种类：文本

Kind: text

• 终端 - 我输出：






text / plain; charset = utf-16le

text/plain; charset=utf-16le

我猜想这个文件的utf-16le编码是关键，因为我期待着NSUTF8文件。
我尝试使用ASCII作为最低公分母。它没有崩溃，但是在一些没有出现在原始文件中的字符中变得柔和。

I am guessing that the utf-16le encoding of the file is the key, as I'm expecting a NSUTF8 file. I attempted to use ASCII as a lowest common denominator. It didn't crash, but fudged in some characters that weren't present in the original file.

NSString *txtFileAsString = [NSString stringWithContentsOfFile:path encoding:NSASCIIStringEncoding error:&errorReading];

所以我尝试首先将文件转换为NSData，希望它可能否定需要识别编码。它不起作用。

So I attempted to convert the file to NSData first, hoping it might negate the need to recognize the encoding. It did not work.

    NSData *txtFileData = [NSData dataWithContentsOfFile:path];
    NSString *txtFileAsString = [[NSString alloc]initWithData:txtFileData encoding:NSUTF8StringEncoding];

这带给我几个问题：



1. 将纯文本文件内容（无论编码）转换为字符串（即最低公分母）都没有通用方式吗？我相信以前是 initWithContentsOfFile 的目的，不幸的是现在已经不推荐了。 ASCIStringEncoding不起作用。


2. 有没有关于将NSUTF16编码的文件转换为一个字符串，我需要处理不同于NSUTF8？

假设文件实际上是URF16LE，为什么以下建议不工作？
1. Is there not a universal way to convert Plain Text file contents, regardless of encoding, to a string (i.e. lowest common denominator)? I believe that used to be the purpose initWithContentsOfFile , which unfortunately is now deprecated. ASCIStringEncoding didn't work.
2. Is there anything about converting an NSUTF16 encoded file to a string that I would need to handle differently than if it were NSUTF8?

3. Assuming the file is in fact URF16LE, why does the following suggestion not work either?

NSString *txtFileAsString = nil;
if (path !=nil) {
  NSData *txtFileData = [NSData dataWithContentsOfFile:path];
  NSString *txtFileAsString = [[NSString alloc]initWithData:txtFileData encoding:NSASCIIStringEncoding];
if (!txtFileAsString) {
  txtFileAsString = [[NSString alloc] initWithData:txtFileData encoding:NSUTF8StringEncoding];
}
if (!txtFileAsString) {
  txtFileAsString = [[NSString alloc] initWithData:txtFileData encoding:NSUTF16StringEncoding];
}
if (!txtFileAsString) {
  txtFileAsString = [[NSString alloc] initWithData:txtFileData encoding:NSUTF16LittleEndianStringEncoding];
}
if (!txtFileAsString) {
  txtFileAsString = [[NSString alloc] initWithData:txtFileData encoding:NSUTF16BigEndianStringEncoding];
}
if (!txtFileAsString) {
  txtFileAsString = [[NSString alloc] initWithData:txtFileData encoding:NSUTF32StringEncoding];
}
if (!txtFileAsString) {
  txtFileAsString = [[NSString alloc] initWithData:txtFileData encoding:NSUTF32LittleEndianStringEncoding];
}
if (!txtFileAsString) {
  txtFileAsString = [[NSString alloc] initWithData:txtFileData encoding:NSUTF32BigEndianStringEncoding];
}}







推荐答案

有时 stringWithContentsOfFile：usedEncoding：error：可以做这个工作（esp如果文件有一个字节顺序标记）：

Sometimes stringWithContentsOfFile:usedEncoding:error: can do the job (esp if the file has a Byte Order Mark):

NSError *error;
NSStringEncoding encoding;
NSString *string = [NSString stringWithContentsOfFile:path usedEncoding:&encoding error:&error];

请注意，使用 usedEncoding 与类似命名的方法混淆，只有一个编码参数。

Note, this rendition with usedEncoding should not be confused with the similarly named method that just has a encoding parameter.

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