Cocoa iPhone Programming: Encoding/Decoding NSString

Question

Is their a method to encode/decode HTML and URL (in Xcode, using Objective-C)?

[NSString stringWithContentsOfFile:<#(NSString *)path#> encoding:<#(NSStringEncoding)enc#> error:<#(NSError **)error#>]

This doesn't seem to work how i expected. I thought it will convert special characters like "<" to equivalent HTML entities i.e. "<" in this case.

Here's a reference to the w3school link related to this topic (general):

HTML URL Encoding Reference

HTML Entities Reference

Thanking in anticipation.

Answer 1

Returns a representation of the receiver using a given encoding to determine the percent escapes necessary to convert the receiver into a legal URL string.

- (NSString *)stringByAddingPercentEscapesUsingEncoding:(NSStringEncoding)encoding

and

Returns a new string made by replacing in the receiver all percent escapes with the matching characters as determined by a given encoding.

- (NSString *)stringByReplacingPercentEscapesUsingEncoding:(NSStringEncoding)encoding

Answer 2

The method you cite reads a file from disk with a given character encoding (such as UTF-8 or ASCII). It has nothing to do with URL or HTML escaping.

If you want to add URL percent escapes, you want this method:

[myString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]

Make sure you read the documentation about this method, because there are certain subtleties about what it escapes and what it leaves alone. In some cases, you may have to use the more complex, but more flexible, CFURLCreateStringByAddingPercentEscapes(). (If you do, note that you can cast CFStringRef to NSString * and vice versa.)

There's nothing built in that I know of to do XML/HTML-style entity escaping, but this function ought to handle the basics:

NSString * convertToXMLEntities(NSString * myString) {
    NSMutableString * temp = [myString mutableCopy];

    [temp replaceOccurrencesOfString:@"&"
                          withString:@"&"
                             options:0
                               range:NSMakeRange(0, [temp length])];
    [temp replaceOccurrencesOfString:@"<"
                          withString:@"&lt;"
                             options:0
                               range:NSMakeRange(0, [temp length])];
    [temp replaceOccurrencesOfString:@">"
                          withString:@"&gt;"
                             options:0
                               range:NSMakeRange(0, [temp length])];
    [temp replaceOccurrencesOfString:@"\""
                          withString:@"&quot;"
                             options:0
                               range:NSMakeRange(0, [temp length])];
    [temp replaceOccurrencesOfString:@"'"
                          withString:@"&apos;"
                             options:0
                               range:NSMakeRange(0, [temp length])];

    return [temp autorelease];
}

Answer 3

To do HTML/XML entity encoding, you can use a CFMutableString function:

NSString *result = .....;
CFStringTransform((CFMutableStringRef)result, NULL, kCFStringTransformToXMLHex, false);

By setting the last parameter of CFStringTransform to true, it should work for decoding (hex) entities as well.