I am new in objective c. I want to replace the content of mutable string I am using code as
NSMutableString *myMutableStringObj = [myMutableStringObj stringByReplacingOccurrencesOfString:#" & " withString:#"And"];
But It Shows me warning
Incomparable pointer types assigning to NSMutableString * from NSString *
Any Suggestion about this. I am using MutableString.
It tells you this function returns NSString *. If you want to clean that warning. Just do like this:
NSMutableString *myMutableStringObj = [[myMutableStringObj stringByReplacingOccurrencesOfString:#" & " withString:#"And"] mutableCopy];
See the method signeture from NSString Class.
- (NSString *)stringByReplacingOccurrencesOfString:(NSString *)target
withString:(NSString *)replacement
this method return NSString object.
So you need to convert result into mutalbe string or catch the result in NSString.
Read the documentation for NSString and NSMutableString. That doesn't only apply to you, but to anyone answering here so far. The answers on this thread have been absolutely depressing.
There are methods that can be used for NSString but also work with NSMutableString which create a new, immutable string based on a previous string. Typically methods starting with "stringBy..." will be creating a new string.
And there are methods, in the NSMutableString interface, which modify the contents of an existing NSMutableString. Like "replaceOccurencesOfString".
Read the documentation and pick what is right for you. A method starting with "stringBy" is not going to modify your mutable string, it's creating a new immutable one. To modify a string, use the methods from the NSMutableString interface. Fortunately the compiler tells you when you use the wrong method.
plz use this code
NSMutableString * str1 = [NSMutableString stringWithString:#"Hello Testing"];
str1 = [[str1 stringByReplacingOccurrencesOfString:#"T" withString:#"B"] mutableCopy];
NSLog(#"%#",str1);
Related
I am trying to replace instances of 's with s or alternatively instances of s with 's. However, the result of the code below is an empty string. What could I be doing wrong?
NSString *myStr = #"Eat at Joe's";
NSString *newStr = [myStr stringByReplacingOccurrencesOfString:#"\'s" withString:#"s"];
//edited as per Vadian
NSLog(#"newStr:%#",newStr); //logs as newStr:
You forgot the placeholder
NSLog(#"newStr: %#", newStr);
Don't you get the warning
Data argument not used by format string
I am simply writing the following code for testing purpose:
NSString *aStr = [[NSString alloc] initWithFormat:#"Foo"];
aStr = [aStr initWithFormat:#"Bar"];//Crashed here
I am getting the following error:
*** initialization method -initWithFormat:locale:arguments: cannot be sent to an abstract object of class __NSCFString: Create a concrete instance!
If i write the following code same thing happen
NSString *aStr = [NSString alloc];
aStr = [aStr initWithFormat:#"Foo"];
aStr = [aStr initWithFormat:#"Bar"]; //Crashed here
By google I come to know that initWithFormat will return the NSCFString Object.
My question is if NSCFString is derived class of NSString then why I cannot invoke the initWithFormat method on NSCFString. If it is possible to stop the visibility how can I implement in the code without overriding the method in NSCFString(Derived Class).
In simple word If NSCFString is derived class of NSString then why i cannot call the base class (initWithFormat) method on that?
I believe that what's happening is that the [NSString initWithFormat:] method is noticing that you have not provided any format specifiers so there is no NSString object that needs building, so it's simply returning the constant NSString object you pass in (#"Foo"):
NSString *aStr = [NSString alloc];
aStr = [aStr initWithFormat:#"Foo"];
So aStr is now of type NSCFString. This is the cause of the crash:
aStr = [aStr initWithFormat:#"Bar"]; //Crashed here
However you should never be calling an init method on an existing object, so to correct the crash use:
aStr = [[NSString alloc] initWithFormat:#"Bar"];
and use format specifiers as you may as well just do:
aStr = #"Foo";
aStr = #"Boo";
which is the same thing only clearer, uses less code and has better performance.
As per Documentation it returns an NSString object initialized by using a given format string as a template into which the remaining argument values are substituted.
And also you need to use like that below :-
NSString *aStr = [[NSString alloc] initWithFormat:#"%#,%#",#"Foo",#"Bar"];
NSLog(#"%#",aStr);
You are asking "why". Besides the answer "calling init twice on the same object is baaaad" which you ignored, NSString is a class cluster.
[NSString alloc] returns a generic object that isn't really usable as a string but expects an init method to be called. Let's think about something obvious: NSString objects are immutable, but the result of [NSString alloc] cannot be immutable, because otherwise it would be impossible to store a value, right?
That init method will actually return a different object that doesn't accept init methods anymore. While [NSString alloc] is a very flexible object that could do anything, after a call to an init method you get an object back that contains a string that can never be modified again.
(Apple may have implemented this differently from what I say or may change their implementation. Nevertheless, they can and will do things that stop you from doing something stupid).
And a warning: Don't even think about subclassing NSString. I can guarantee that you won't get anything cobbled together that works.
I want to add multiple NSStrings yo an NSMutableString to construct a list of strings.
This is my code in a method that takes an NSDictionary and grabs the value out of it - it then stores it in an NSString, From there I append the string to the NSMutableString. When running this method for the first time it works. However, when I call the method again, it replaces the last string that was in the NSMutableString.
Here is the code:
NSString *userId = [NSString stringWithFormat:#"%#,", parameters[#"userId"]];
self.alluserIds = [NSMutableString string];
[self.alluserIds appendString:userId];
Can anyone tell me what I am doing wrong?
self.alluserIds is declared strong.
This:
self.alluserIds = [NSMutableString string];
is creating a new mutable string. It should be done once, before you want to use the mutable string, and not done again until you want to restart (because recreating the mutable string destroys the old instance you had).
This is happened because you call:
self.alluserIds = [NSMutableString string];
This create new string and assign it to self.alluserIds. You should call it just once in for example init method or viewDidLoad.
You should initialize with the string you are using and it should be a single initialization your code should look like below.
NSString *userId = [NSString stringWithFormat:#"%#,", parameters[#"userId"]];
if(!self.alluseIds)
self.alluserIds = [[NSMutableString alloc] initWithString:userId]; //ONLY Initialization
else
[self.alluserIds appendString:userId];
Hope this helps
I don't know your data-structure, but if you might have all userids in an array you could join them together with componentsJoinedByString::
NSArray *pathArray = [NSArray arrayWithObjects:#"here", #"be", #"dragons", nil];
NSLog(#"%#",[pathArray componentsJoinedByString:#" "]);
Don't use mutable strings(and mutable collections too) except cases you really need it: http://rypress.com/tutorials/objective-c/data-types/nsstring.html (When To Use Mutable Strings) You have to use them when you want to make a lot of operations. Immutable collections are slower because you create new instance when append another string.
How to do this with NSString:
self.alluserIds = [self.alluserIds stringByAppendingString: userId];
I am new to the ios development.I was checking the NSString and where I had found out that it was excessed using the multiple ways which is as under
1) NSString *theString = #"hello";
2) NSString *string1 = [NSString stringWithString:#"This is"];
3) NSString *string =[[NSString alloc]init];
string =#"Hello";
Now I am confused with above three and would like to know the differences between then?
Yes all three are ways to create string...I try to explain you one by one.
One think you must remember that in Objective-c string is represented by #"".
whatever comes double quotes is string eg #"Hello" is string. #"" is basically literal to create NSString.
NSString *theString = #"hello";
EDIT:
In this statement we are creating an NSString constant. Objective-C string constant is created at compile time and exists throughout your program’s execution.
2. NSString *string1 = [NSString stringWithString:#"This is"];
In this statement again, we are creating an autorelease object of NSString, but here a slide diff. than the first case. here we are using another NSString object to create a new autorelease object of NSString. So generally we use stringWithString method when we already have NSString Object and we want another NSString object with similar content.
3. NSString *string =[[NSString alloc]init];
string =#"Hello";
Here, In first statement you are creating a NSString Object that you owned and it is your responsibility to release it (In non-ARC code), once you done with this object.
Second statement is similar to case 1, by string literal you are creating string Object.
but when you put these two statements together it causes you memory-leak(In non-ARC code), because in statement one you are allocating & initiating memory for new string object and right after in second statement you are again assigning a new string object to the same string reference.
1) and 2) is the same. there is no difference. [NSString stringWithString: str] just does nothing and returns str if str is immutable already. via this link
3) you create empty NSString pointer. after you assign this string with ' = ' is same way with 1) and it alloc memory to your NSString. You can watch this NSString pointer in 3) and you see pointer was changed:
NSString *string =[[NSString alloc]init];
printf("\n string_1-> = %p\n", string );
string = #"Hello";
printf("\n string_2-> = %p\n", string );
OK, first off, the syntax #"blah" is an Objective-C literal to create an NSString. Essentially it is an NSString.
Also, there are two parts to each statement. The declaration of the string variable NSString *string and the instantiation string = <something>.
So...
This is how you would do it most of the time. You declare the variable and set it using the objective-c literal.
This adds a bit of redundancy and you wouldn't really use it like this. You'd maybe use it with a substring or something from another string. As it is you are essentially creating two objects here. The first is [NSString stringWithString:<>]; and the second is #"This is".
This is a bit odd. You are first creating an empty string #"" and then you are replacing this string with #"Hello". Don't do this. There is no point. You may as well just do number 1 as the result is the same.
All three will work but in these exact cases you'd be better off using the first.
Hello everyone I am trying find a string inside a string
lets say I have a string:
word1/word2/word3
I want to find the word from the end of the string to the last "/"
so what I will get from that string is:
Word3
How do I do that?
Thanks!
You are looking for the componentsSeparatedByString: method
NSString *originalString = #"word1/word2/word3";
NSArray *separatedArray = [originalString componentsSeparatedByString:#"/"];
NSString *lastObject = [separatedArray lastObject]; //word3
once check this one By using this one you'l get last pathcomponent values,
NSString* theFileName = #"how /are / you ";
NSString *str1=[theFileName lastPathComponent];
NSLog(#"%#",str1);
By using lastPathComponent you'l get the last path component directly no need to take array for separate the string.
you must use NSScanner class to split substring.
check this.
Objective C: How to extract part of a String (e.g. start with '#')
NSString *string = #"word1/word2/word3"
NSArray *arr = [string componentsSeperatedByString:#"/"];
NSSting *str = [arr lastObject];
You can find it also with this way:
NSMutableString *string=[NSMutableString stringWithString:#"word1/word2/word3"];
NSRange range=[string rangeOfString:#"/" options:NSBackwardsSearch];
NSString *subString=[string substringFromIndex:range.location+1];
NSRegularExpression or NSString rangeOfString:options:range:locale: (with options to search backwards).
The answer really depends on exactly what the input string will contain (how consistent it is).