NSString NSMutableString字符串 用一个字符替换其中的某个字符 字符串

NSString ：：：：：
    NSString *time = [[timeString stringByReplacingOccurrencesOfString:@"T" withString:@" "] substringToIndex:19];
NSMutableString：：：：：   
 NSMutableString *string = [[NSMutableString alloc]initWithString:timeString] ;
    NSRange range = NSMakeRange(0, [string length]);
    [string replaceOccurrencesOfString:@"T" withString:@" " options:NSCaseInsensitiveSearch range:range];