How can I escape this regex properly in Objective-C? - iphone

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];