如何在Objective-C中正确地逃避这个正则表达式？

Question

I have the following regex I would like to escape in Objective-C

/\B\$((?:[0-9]+(?=[a-z])|(?![0-9\.\:\_\-]))(?:[a-z0-9]|[\_\.\-\:](?![\.\_\.\-\:]))*[a-z0-9]+)/ig;

Not exactly sure how to escape it so it works in Objective-C

Update:

NSString* pattern = @"/\\B\\$((?:[0-9]+(?=[a-z])|(?![0-9\\.\\:\\_\\-]))(?:[a-z0-9]|[\\_\\.\\-\\:](?![\\.\\_\\.\\-\\:]))*[a-z0-9]+)/ig;";
NSRegularExpression *usernameRegex = [[[NSRegularExpression alloc] initWithPattern:pattern
                                                                  options:NSRegularExpressionCaseInsensitive 
                                                                    error:nil];
                                                                        error:nil];

Gives me an error about Parse Issue - Unexpected Identifier

Answer 1

Backslashes are used as escape characters in C strings. To make a regexp that contains backslashes as regex escapes, you need to double them.

Answer 2

Following on from the correct solution by millimoose, here is a NSString category method I use to escape black slashes for Regex patterns in Objective C.

+ (NSString *)escapeBackslashes:(NSString *)regexString
{
    NSError *error = NULL;
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"\\\\" options:NSRegularExpressionCaseInsensitive | NSRegularExpressionDotMatchesLineSeparators | NSRegularExpressionAnchorsMatchLines | NSRegularExpressionAllowCommentsAndWhitespace error:&error];
    if (error == NULL)
    {
        return [regex stringByReplacingMatchesInString:regexString options:0 range:NSMakeRange(0, [regexString length]) withTemplate:@"\\\\"];
    }
    else
    {
        return regexString;
    }
}

Usage example:

NSString* pattern = [NSString escapeBackslashes:pattern];