Is there any efficient way to replace characters in NSString

Question

I have 20 lines of code that replaces multiple values of NSString as below.

[resultstring
    replaceOccurrencesOfString:@"&amp;"
    withString:@"&"
    options:NSLiteralSearch
    range:NSMakeRange(0, [resultstring length])
];

The problem is that it is takes some noticeable amount of time (20ms) for executing the code. Is there any better approach to write the NSString replacement code.

it sounds like you want to escape HTML entities. Check this out http://stackoverflow.com/questions/659602/objective-c-html-escape-unescape — Gabriele Petronella, Sep 11 '13 at 01:18
Well, you *could* break down and actually have a shot at that they call "programming". — Hot Licks, Sep 11 '13 at 01:19

score 2 · Accepted Answer · edited May 23 '17 at 11:56

replaceOccurrencesOfString:... will traverse the string each time you call it.

An alternative which should make the replacement faster is to manually traverse the string just once and build a new string along the way.

Here's an example, although there's probably still room for further optimization

- (NSString *)encodeEntity:(NSString *)string {
    NSUInteger length = string.length;
    NSMutableString *encodedString = [NSMutableString stringWithCapacity:length];
    unichar buffer[length + 1];
    [string getCharacters:buffer range:(NSRange){0, length}];
    for(NSUInteger i = 0; i < length; i++) {
        char current = buffer[i];
        switch(current) {
            case '&':  [encodedString appendString:@"&amp;"];        break;
            case '\"': [encodedString appendString:@"&quot;"];       break;
            case '\'': [encodedString appendString:@"&apos;"];       break;
            case '<':  [encodedString appendString:@"&lt;"];         break;
            case '>':  [encodedString appendString:@"&gt;"];         break;
            default:   [encodedString appendFormat:@"%c", current];  break;
        }
    }
    return encodedString;
}

Also if your specific issue is to escape XML entities, this question may be useful: Objective C HTML escape/unescape

Is there any efficient way to replace characters in NSString

1 Answers1