Is there a general purpose function in Objective-C that I can plug into my project to simplify concatenating NSStrings and ints?
[NSString stringWithFormat:#"THIS IS A STRING WITH AN INT: %d", myInt];
That's typically how I do it.
Both answers are correct. If you want to concatenate multiple strings and integers use NSMutableString's appendFormat.
NSMutableString* aString = [NSMutableString stringWithFormat:#"String with one int %d", myInt]; // does not need to be released. Needs to be retained if you need to keep use it after the current function.
[aString appendFormat:#"... now has another int: %d", myInt];
NSString *s =
[
[NSString alloc]
initWithFormat:#"Concatenate an int %d with a string %#",
12, #"My Concatenated String"
];
I know you're probably looking for a shorter answer, but this is what I would use.
string1,x , these are declared as a string object and integer variable respectively. and if you want to combine both the values and to append int values to a string object and to assign the result to a new string then do as follows.
NSString *string1=#"Hello";
int x=10;
NSString *string2=[string1 stringByAppendingFormat:#"%d ",x];
NSLog(#"string2 is %#",string2);
//NSLog(#"string2 is %#",string2); is used to check the string2 value at console ;
It seems the real answer is no - there is no easy and short way to concatenate NSStrings with Objective C - nothing similar to using the '+' operator in C# and Java.
Related
I understand pointers work with addresses and not the data itself. This is why I need to use the address-of (&) operator below as I need to assign the address of num to the pointer and not the actual value of num (40).
int num = 40;
int *numPtr = #
Therefore i'm confused as to why I can do this.
NSString *str = #"hello";
I've created a pointer str but instead of giving it an address i'm able to assign it some data, a literal string.
I thought pointers could only hold memory addresses so why am I able to directly assign it some data?
For someone trying to get their head around pointers and objects this is very confusing.
No you are not assigning a literal string to it, # makes a NSString object with the string value hello.
In most C languages strings are just an array of char, where char is a primitive type like int like in your example.
There is a reason you put an # before string literals (when you want an NSString and not a C string) in objective-c
#"String" is basically equivalent to [NSString stringWithCString:"string"] which returns a pointer to an NSString object containing the value "string"
It is the same way 1 is a c type integer, but #1 is a NSNumber representing the value of 1. If you see an # it means "this is shorthand for creating an object". (#[] for NSArrays, #{} for NSDictionarys, #(), #123, #YES, #NO for NSNumbers, and #"" for NSString)
C does not have strings. Usually char arrays are used to represent them.
NSString *str = #"hello";
can be thought of as short hand (literal) for:
char charArray[] = "hello";
NSString *str = [[NSString alloc] initWithBytes:charArray length:sizeof(charArray) encoding:NSUTF8StringEncoding]; // disregard character encoding for this example
or
unichar bla[] = {'h', 'e', 'l', 'l', 'o'};
str = [[NSString alloc] initWithCharacters:bla length:sizeof(bla)];
So an object is created and thus you need a pointer.
I got a NSMutableArray object with int values
and I can get a certain value via :
int *v0=[[[arrayObj objectAtIndex:0] intValue];
there is no problem.
But
I got a NSMutableArray object with NSString values
and I cannot get a certain value via :
NSString *v0=[[[arrayObj objectAtIndex:0] stringValue];
//raises error
I want to learn and understand exactly what stringValue for... and why this error occurs ?
NSString *v0=[arrayObj objectAtIndex:0];
works as expected.I asusme its some kind of pointer with null terminated so it can leech value.
Im not sure this line is also unicode/encoded string safe code.
in conclusion:
want to know the purpose of stringValue with some lines o code snippets
I got a NSMutableArray object with int values
That's not possible, Cocoa arrays always contain objects. You probably have an array of NSNumber objects that wrap the integers, like:
NSArray *arrayOfNumbers = #[#1, #2, #3];
NSNumber objects have an intValue method, so this works:
int value = [arrayOfNumbers[0] intValue];
On the other hand when you have an array of strings ...
NSArray *arrayOfStrings = #[#"1", #"2", #"3"];
... you want to access individual elements directly, without converting the string object to something else:
NSString *element = arrayOfStrings[0];
NSString objects do not understand the stringValue method:
[arrayOfStrings[0] stringValue]; // crash: does not recognize selector
Back at the beginning, our NSNumber objects from the first array do understand stringValue. You can use it to convert the number to a string:
NSString *intString = [arrayOfNumbers[0] stringValue];
To make the confusion perfect, NSString also understand the intValue message:
int value = [arrayOfStrings[0] intValue];
Here intValue means to try to convert the string to a plain C int value.
The error you will be getting (but failing to post with your question) will be Unknown selector sent to instance and this is because NSString doesn't have a stringValue method.
The approach you suggest is correct:
NSString *v0 = [arrayObj objectAtIndex:0];
EDIT (prompted by #Answerbot's answer):
The reason you are confused is that [NSString intValue] is used to convert the string value to an integer, as long as the string represents an integer (i.e. #"123"). However you don't need this for string as the object is already a string. It's therefore not provided.
I'm struggling with concatenating NSStrings and ints. In isolation the below code works great. It returns "This is a test string with an int 10"
int myInt =10;
NSString *newstring =
[NSString stringWithFormat: #"This is a test string with an int %i", myInt];
NSLog(#"%#", newstring);
However when I put the below code into my project i get an error: Implicit conversion of int to NSString is disallowed with arc."
[_mycrop setTempLeft: (#"left value %i is %i", count, [_mycrop leftValue])];
Could anybody suggest where I'm going wrong? Although im passing in 2 variables, to my mind both are essentially the same.
The code "in isolation" is very different from the second code.
You have to use stringWithFormat: in the second example too.
[_mycrop setTempLeft:[NSString stringWithFormat:#"left value %i is %i", count, [_mycrop leftValue]]];
Or with two lines but easier to understand:
NSString *tempLeft = [NSString stringWithFormat:#"left value %i is %i", count, [_mycrop leftValue]];
[_mycrop setTempLeft:tempLeft];
Some documentation: Apple String Programming Guide - Formatting String Objects
I have an NSString and fail to apply the following statement:
NSString *myString = #"some text";
[myString stringByAppendingFormat:#"some text = %d", 3];
no log or error, the string just doesn't get changed. I already tried with NSString (as documented) and NSMutableString.
any clues most welcome.
I would suggest correcting to (documentation):
NSString *myString = #"some text";
myString = [myString stringByAppendingFormat:#" = %d", 3];
From the docs:
Returns a string made by appending to the receiver a string constructed from a given format string and the following arguments.
It's working, you're just ignoring the return value, which is the string with the appended format. (See the docs.) You can't modify an NSString — to modify an NSMutableString, use -appendFormat: instead.
Of course, in your toy example, you could shorten it to this:
NSString *myString = [NSString stringWithFormat:#"some text = %d", 3];
However, it's likely that you need to append a format string to an existing string created elsewhere. In that case, and particularly if you're appending multiple parts, it's good to think about and balance the pros and cons of using a mutable string or several immutable, autoreleased strings.
Creating strings with #"" always results in immutable strings. If you want to create a new NSMutableString do it as following.
NSMutableString *myString = [NSMutableString stringWithString:#"some text"];
[myString appendFormat:#"some text = %d", 3];
I had a similar warning message while appending a localized string. This is how I resolved it
NSString *msgBody = [msgBody stringByAppendingFormat:#"%#",NSLocalizedString(#"LOCALSTRINGMSG",#"Message Body")];
I want to compare the value of an NSString to the string "Wrong". Here is my code:
NSString *wrongTxt = [[NSString alloc] initWithFormat:#"Wrong"];
if( [statusString isEqualToString:wrongTxt] ){
doSomething;
}
Do I really have to create an NSString for "Wrong"?
Also, can I compare the value of a UILabel's text to a string without assigning the label value to a string?
Do I really have to create an NSString for "Wrong"?
No, why not just do:
if([statusString isEqualToString:#"Wrong"]){
//doSomething;
}
Using #"" simply creates a string literal, which is a valid NSString.
Also, can I compare the value of a UILabel.text to a string without assigning the label value to a string?
Yes, you can do something like:
UILabel *label = ...;
if([someString isEqualToString:label.text]) {
// Do stuff here
}
if ([statusString isEqualToString:#"Wrong"]) {
// do something
}
Brian, also worth throwing in here - the others are of course correct that you don't need to declare a string variable. However, next time you want to declare a string you don't need to do the following:
NSString *myString = [[NSString alloc] initWithFormat:#"SomeText"];
Although the above does work, it provides a retained NSString variable which you will then need to explicitly release after you've finished using it.
Next time you want a string variable you can use the "#" symbol in a much more convenient way:
NSString *myString = #"SomeText";
This will be autoreleased when you've finished with it so you'll avoid memory leaks too...
Hope that helps!
You can also use the NSString class methods which will also create an autoreleased instance and have more options like string formatting:
NSString *myString = [NSString stringWithString:#"abc"];
NSString *myString = [NSString stringWithFormat:#"abc %d efg", 42];