如何在 macOS 上取消转义反斜杠？

Question

Localized.strings 文件可能包含转义字符，例如 \n 和 \"。

我如何有效地取消转义？

我知道我可以编写自己的函数来查找 \ 并将其删除，然后继续搜索下一个字符（这样我就不会将 \\ 变成空），但这不会t 处理特殊的转义方法，例如八进制字符数字（例如，\012 用于 LF）和可能的其他形式。

我认为NSString 会为此提供一个功能，但我找不到任何功能。

实际上，这似乎与NSString strip regular \ escape characters how? 重复，但该问题有很多错误答案，没有一个正确答案。并且用户不再活跃，这意味着没有人会在那里接受正确的答案。 SO应该如何处理？

Answer 1

这是一个自写的 ObjC 版本，适用于大多数情况。它为 NSString 定义了一个unescaped 方法。

#import <Cocoa/Cocoa.h>

@interface NSString (BackslashUnescaping)
- (NSString*) unescaped;
@end

@implementation NSString (BackslashUnescaping)

- (NSString*) unescaped
{
    NSString *text = self;
    NSInteger charIndex = 0;
    while (true) {
        NSInteger textLen = text.length;
        if (charIndex >= textLen) {
            break;
        }
        NSRange remainingRange = NSMakeRange (charIndex, textLen-charIndex);
        NSRange charRange = [text rangeOfString:@"\\"options:0 range:remainingRange];
        if (charRange.length == 0) {
            // no more backslashes -> done
            break;
        }
        charIndex = charRange.location + 1;
        if (charIndex >= textLen) {
            // reached end of string -> exit loop
            break;
        }
        // check char following the backslash
        unichar nextChar = [text characterAtIndex:charIndex];
        unichar replacementChar;
        NSInteger skipLen = 1;
        if (nextChar >= 'a' && nextChar <= 'z') {
            if (nextChar == 'n') {
                replacementChar = '\n'; // LF
            } else if (nextChar == 'r') {
                replacementChar = '\r'; // CR
            } else if (nextChar == 't') {
                replacementChar = '\t'; // TAB
            } else if (nextChar == 'x') {
                // A hex char code
                const NSInteger xtraLen = 2;
                if (charIndex+xtraLen >= textLen) break;
                // Note: Does not make sure that both chars are valid hex chars
                NSString *code = [text substringWithRange:NSMakeRange(charIndex+1, 2)];
                char ch = strtol(code.UTF8String, NULL, 16);
                replacementChar = ch;
                skipLen += xtraLen;
            } else if (nextChar == 'u') {
                // A unicode char code
                const NSInteger xtraLen = 4;
                if (charIndex+xtraLen >= textLen) break;
                // Note: Does not make sure that all four chars are valid hex chars
                NSString *code = [text substringWithRange:NSMakeRange(charIndex+1, 4)];
                unichar ch = strtol(code.UTF8String, NULL, 16);
                replacementChar = ch;
                skipLen += xtraLen;
            } else {
                // an unknown escape code - this should be fixed
                NSAssert(false, @"There's a case missing for escaping \\%c", nextChar);
            }
        } else if (nextChar >= '0' && nextChar <= '9') {
            unichar nextChar2 = 0;
            if (charIndex > textLen) {  // get the second octal char
                nextChar2 = [text characterAtIndex:charIndex+1];
            }
            if (nextChar == '0' && (nextChar2 < '0' || nextChar2 > '9')) {
                // A short NUL (\0) char
                replacementChar = 0;
            } else {
                // An octal char code
                const NSInteger xtraLen = 2;
                if (charIndex+xtraLen >= textLen) break;
                // Note: Does not make sure that the last char is a valid octal char
                NSString *code = [text substringWithRange:NSMakeRange(charIndex, 3)];
                char ch = strtol(code.UTF8String, NULL, 8); // https://*.com/a/12820646/43615
                replacementChar = ch;
                skipLen += xtraLen;
            }
        } else {
            // Handle all generic escapes, like for \\ and \"
            replacementChar = nextChar;
        }
        #if 0 // Use string concatenation
            charIndex += skipLen-1;
            NSString *head = [text substringToIndex:charRange.location];
            NSString *tail = [text substringFromIndex:charIndex+1];
            text = [NSString stringWithFormat:@"%@%C%@", head, replacementChar, tail];
        #else // Use a mutable string
            if (text == self) {
                text = text.mutableCopy;
            }
            NSRange replacedRange = NSMakeRange(charRange.location, skipLen+1);
            NSString *replacement = [NSString stringWithCharacters:&replacementChar length:1];
            [(NSMutableString*)text replaceCharactersInRange:replacedRange withString:replacement];
            charIndex += 1;
        #endif 
    }
    return text;
}

@end 

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSArray *testValues = @[
            @"CR:\\rLF:\\n",
            @"\\\"quoted\\\"",
            @"Backslash: \\\\",
            @"Octal x (\170):\\170",
            @"Hex x (\x78):\\x78",
            @"Unicode Ф (\u0424):\\u0424",
            @"NUL char:\\0.",
            @"Bad Hex:\\x7x",   // this is not detected being invalid
            @"Bad Hex:\\x7",
            @"Incomplete :\\13"
        ];
        for (NSString *s in testValues) {
            NSString *s2 = [NSString stringWithFormat:@"Escaped:   %@\nUnescaped: %@", s, s.unescaped];
            printf("\n%s\n", s2.UTF8String);
        }
    }
    return 0;
}