How to check if NSString begins with a certain character

Question

You can use the -hasPrefix: method of NSString:

Objective-C:

NSString* output = nil;
if([string hasPrefix:@"*"]) {
    output = [string substringFromIndex:1];
}

Swift:

var output:String?
if string.hasPrefix("*") {
    output = string.substringFromIndex(string.startIndex.advancedBy(1))
}

You can use:

NSString *newString;
if ( [[myString characterAtIndex:0] isEqualToString:@"*"] ) {
     newString = [myString substringFromIndex:1];
}

hasPrefix works especially well. for example if you were looking for a http url in a NSString, you would use componentsSeparatedByString to create an NSArray and the iterate the array using hasPrefix to find the elements that begin with http.

NSArray *allStringsArray = 
   [myStringThatHasHttpUrls componentsSeparatedByString:@" "]

for (id myArrayElement in allStringsArray) {
    NSString *theString = [myArrayElement description];
    if ([theString hasPrefix:@"http"]) {
        NSLog(@"The URL  is %@", [myArrayElement description]);
    }

}

hasPrefix returns a Boolean value that indicates whether a given string matches the beginning characters of the receiver.

- (BOOL)hasPrefix:(NSString *)aString, 

parameter aString is a string that you are looking for Return Value is YES if aString matches the beginning characters of the receiver, otherwise NO. Returns NO if aString is empty.

As a more general answer, try using the hasPrefix method. For example, the code below checks to see if a string begins with 10, which is the error code used to identify a certain problem.

NSString* myString = @"10:Username taken";

if([myString hasPrefix:@"10"]) {
      //display more elegant error message
}

Use characterAtIndex:. If the first character is an asterisk, use substringFromIndex: to get the string sans '*'.