从 NSString 的第一行删除换行符

Question

How can I remove the first \n character from an NSString?

Edit: Just to clarify, what I would like to do is: If the first line of the string contains a \n character, delete it else do nothing.

ie: If the string is like this:

@"\nhello, this is the first line\nthis is the second line"

and opposed to a string that does not contain a newline in the first line:

@"hello, this is the first line\nthis is the second line."

I hope that makes it more clear.

Answer 1

[string stringByTrimmingCharactersInSet:[NSCharacterSet newlineCharacterSet]]

will trim your string from any kind of newlines, if that's what you want.

[string stringByReplacingOccurrencesOfString:@"\n" withString:@"" options:0 range:NSMakeRange(0, 1)]

will do exactly what you ask and remove newline if it's the first character in the string

Answer 2

This should do the trick:

NSString * ReplaceFirstNewLine(NSString * original)
{
    NSMutableString * newString = [NSMutableString stringWithString:original];

    NSRange foundRange = [original rangeOfString:@"\n"];
    if (foundRange.location != NSNotFound)
    {
        [newString replaceCharactersInRange:foundRange
                                 withString:@""];
    }

    return [[newString retain] autorelease];
}

Answer 3

Rather than creating an NSMutableString and using a few retain/release calls, you can use only the original string and simplify the code by using the following instead: (requires 10.5+)

NSRange foundRange = [original rangeOfString:@"\n"];
if (foundRange.location != NSNotFound)
    [original stringByReplacingOccurrencesOfString:@"\n"
                                        withString:@""
                                           options:0 
                                             range:foundRange];

(See -stringByReplacingOccurrencesOfString:withString:options:range: for details.)

The result of the last call method call can even be safely assigned back to original IF you autorelease what's there first so you don't leak the memory.