How to append a NSMutableString with a NSMutableString?

Question

NSMutableString *str, *str1;

//allocation here

i am using [str appendString:str1] is not working. [str appendFormat:str1] is not working.

So, how to append a NSMutableString with another NSMutableString.

@str is an empty string initialize to nil. str1 has some value. [str appendString str1] returns null

In order for us to help you, we would need to know what "not working" means in your case, because our crystal ball is currently not working :) According to Apples documentation, both methods should do what you are trying to do ( http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSMutableString_Class/Reference/Reference.html#//apple_ref/occ/instm/NSMutableString/appendString: ) — fresskoma, Aug 30 '10 at 11:45
After alloc method, does you call initWithXXX or init, to initialize the variable you allocated ? — AechoLiu, Aug 30 '10 at 12:13
Give an example, please. What is the value of `str` before and after the call? — Max Seelemann, Aug 30 '10 at 12:14
@Max, str is an empty string initialize to nil. str1 has some value. [str appendString str1] returns null — user426795, Aug 30 '10 at 12:22

score 21 · Answer 1 · answered Aug 30 '10 at 13:21

Seems like your're sending a message to nil. nil is NOT an object, it's just nothing. Sending a message to nothing just return nothing. In order to append these strings, you need to initialize to an empty string. Like so:

NSMutableString *str = [NSMutableString string];

Then your code will work. Like so:

[str appendString:str1];

VdesmedT · Answer 2 · 2010-08-30T13:40:41.920

3

if str == nil, no call are performed because there is no object allocated to receive the message but no exception are raised (messages sent to nil return nil by design in Objective-C).

NSMutableString *str, *str1;

str = [NSMutableString stringWithString:@"Hello "];
str1 = [NSMutableString stringWithString:@"World"]; 

NSMutableString *sayit = [str appendString:str1];

edited Aug 30 '10 at 13:40

answered Aug 30 '10 at 13:35

VdesmedT

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Then how to set my My NSMutableString to null. Because some point of my program i want to set str1 to empty. – user426795 Aug 30 '10 at 14:48
It's maybe time to explain more precisely what you exactly want to do... Btw, Empty and nil are different things – VdesmedT Aug 30 '10 at 21:06
[NSMutableString string] creates an empty mutable string I.e. "" – VdesmedT Aug 31 '10 at 06:52

score 1 · Answer 3 · edited Jun 20 '20 at 09:12

Swift version

Although in Swift it is not the general practice to use NSMutableString, it may at times be necessary. This is how you would do it:

var str: NSMutableString = NSMutableString()
var str1: NSMutableString = "some value"
str.appendString(str1 as String) // str = "some value"

Note that the usual way to append a string in Swift is like this:

var str = ""
let str1 = "some value"
str += str1

where str and str1 are inferred to be of type String.

score 0 · Answer 4 · answered Aug 30 '10 at 11:59

NSMutableString *mystring = [NSMutableString stringWithFormat:@"pretty"];
    NSMutableString *appending = [NSMutableString stringWithFormat:@"face"];
    [mystring appendString:appending];

works for me...

are you sure the variables have been allocated (correctly?)? No misspellings?

How to append a NSMutableString with a NSMutableString?

4 Answers4

Swift version

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