Question

I have a really long string, I just want to extract some certain string inside that string. How can I do that?

for example I have:

this is the image <img src="http://vnexpress.net/Files/Subject/3b/bd/67/6f/chungkhoan-xanhdiem2.jpg"> and it is very beautiful.

and yes now i want to get substring this long string and get only http://vnexpress.net/Files/Subject/3b/bd/67/6f/chungkhoan-xanhdiem2.jpg

Please show me how I can do this.

Answer 1

You can use regular expressions for this:

NSRegularExpression* regex = [[NSRegularExpression alloc] initWithPattern:@"src=\"([^\"]*)\"" options:NSRegularExpressionCaseInsensitive error:nil];
NSString *text = @"this is the image <img src=\"http://vnexpress.net/Files/Subject/3b/bd/67/6f/chungkhoan-xanhdiem2.jpg\"> and it is very beautiful.";
NSArray *imgs = [regex matchesInString:text options:0 range:NSMakeRange(0, [text length])];
if (imgs.count != 0) {
    NSTextCheckingResult* r = [imgs objectAtIndex:0];
    NSLog(@"%@", [text substringWithRange:[r rangeAtIndex:1]]);
}

This regular expression is the heart of the solution:

src="([^"]*)"

It matches the content of the src attribute, and captures the content between the quotes (note a pair of parentheses). This caption is then retrieved in [r rangeAtIndex:1], and used to extract the part of the string that you are looking for.