1151
votes

Are there any shortcuts to (stringByAppendingString:) string concatenation in Objective-C, or shortcuts for working with NSString in general?

For example, I'd like to make:

NSString *myString = @"This";
NSString *test = [myString stringByAppendingString:@" is just a test"];

something more like:

string myString = "This";
string test = myString + " is just a test";
30
I'd just like to propose '@+' as a concatenation operator. I'll expect this in the next update to Objective-C, kthxbaipowerj1984
@NicolasMiari This is not the only feature that Objective-C lacks. There are dozens of others. Quoting from the link Jordão posted: "Objective-C is, to be blunt, a primitive language. Compare it to any modern language and you quickly find it lacking." I agree. Objective-C (early 1980s) is C (early 1970s) with the addition of a very simple and not very type-safe kind of OOP. It's ok, but compared with Java or C#, it feels very old-fashioned.jcsahnwaldt Reinstate Monica
@NicolasMiari: Interpreted language? C# and Java are compiled languages. Compiled to bytecode, which is then compiled again to machine code.Joren
Things are changed now : Swift (apple new language) is more straightforwardPradeep
Regarding "type safety", I think it's a problem of style. For someone coming from C#/C++, having heterogeneous arrays of objects of any type might seem odd, but for someone accustomed to Objective-C/Cocoa, it's a form of dynamism and freedom; it is an advantage provided you know what you are doing. Like pretty much everything about C that younger programmers bash these days...Nicolas Miari

30 Answers

628
votes

Two answers I can think of... neither is particularly as pleasant as just having a concatenation operator.

First, use an NSMutableString, which has an appendString method, removing some of the need for extra temp strings.

Second, use an NSArray to concatenate via the componentsJoinedByString method.

1154
votes

An option:

[NSString stringWithFormat:@"%@/%@/%@", one, two, three];

Another option:

I'm guessing you're not happy with multiple appends (a+b+c+d), in which case you could do:

NSLog(@"%@", [Util append:one, @" ", two, nil]); // "one two"
NSLog(@"%@", [Util append:three, @"/", two, @"/", one, nil]); // three/two/one

using something like

+ (NSString *) append:(id) first, ...
{
    NSString * result = @"";
    id eachArg;
    va_list alist;
    if(first)
    {
        result = [result stringByAppendingString:first];
        va_start(alist, first);
        while (eachArg = va_arg(alist, id)) 
        result = [result stringByAppendingString:eachArg];
        va_end(alist);
    }
    return result;
}
155
votes

If you have 2 NSString literals, you can also just do this:

NSString *joinedFromLiterals = @"ONE " @"MILLION " @"YEARS " @"DUNGEON!!!";

That's also useful for joining #defines:

#define STRINGA @"Also, I don't know "
#define STRINGB @"where food comes from."
#define JOINED STRINGA STRINGB

Enjoy.

80
votes

I keep returning to this post and always end up sorting through the answers to find this simple solution that works with as many variables as needed:

[NSString stringWithFormat:@"%@/%@/%@", three, two, one];

For example:

NSString *urlForHttpGet = [NSString stringWithFormat:@"http://example.com/login/username/%@/userid/%i", userName, userId];
52
votes

Create a method:

- (NSString *)strCat: (NSString *)one: (NSString *)two
{
    NSString *myString;
    myString = [NSString stringWithFormat:@"%@%@", one , two];
    return myString;
}

Then, in whatever function you need it in, set your string or text field or whatever to the return value of this function.

Or, to make a shortcut, convert the NSString into a C++ string and use the '+' there.

45
votes

Well, as colon is kind of special symbol, but is part of method signature, it is possible to exted the NSString with category to add this non-idiomatic style of string concatenation:

[@"This " : @"feels " : @"almost like " : @"concatenation with operators"];

You can define as many colon separated arguments as you find useful... ;-)

For a good measure, I've also added concat: with variable arguments that takes nil terminated list of strings.

//  NSString+Concatenation.h

#import <Foundation/Foundation.h>

@interface NSString (Concatenation)

- (NSString *):(NSString *)a;
- (NSString *):(NSString *)a :(NSString *)b;
- (NSString *):(NSString *)a :(NSString *)b :(NSString *)c;
- (NSString *):(NSString *)a :(NSString *)b :(NSString *)c :(NSString *)d;

- (NSString *)concat:(NSString *)strings, ...;

@end

//  NSString+Concatenation.m

#import "NSString+Concatenation.h"

@implementation NSString (Concatenation)

- (NSString *):(NSString *)a { return [self stringByAppendingString:a];}
- (NSString *):(NSString *)a :(NSString *)b { return [[self:a]:b];}
- (NSString *):(NSString *)a :(NSString *)b :(NSString *)c
    { return [[[self:a]:b]:c]; }
- (NSString *):(NSString *)a :(NSString *)b :(NSString *)c :(NSString *)d
    { return [[[[self:a]:b]:c]:d];}

- (NSString *)concat:(NSString *)strings, ...
{
    va_list args;
    va_start(args, strings);

    NSString *s;    
    NSString *con = [self stringByAppendingString:strings];

    while((s = va_arg(args, NSString *))) 
        con = [con stringByAppendingString:s];

    va_end(args);
    return con;
}
@end

//  NSString+ConcatenationTest.h

#import <SenTestingKit/SenTestingKit.h>
#import "NSString+Concatenation.h"

@interface NSString_ConcatenationTest : SenTestCase

@end

//  NSString+ConcatenationTest.m

#import "NSString+ConcatenationTest.h"

@implementation NSString_ConcatenationTest

- (void)testSimpleConcatenation 
{
    STAssertEqualObjects([@"a":@"b"], @"ab", nil);
    STAssertEqualObjects([@"a":@"b":@"c"], @"abc", nil);
    STAssertEqualObjects([@"a":@"b":@"c":@"d"], @"abcd", nil);
    STAssertEqualObjects([@"a":@"b":@"c":@"d":@"e"], @"abcde", nil);
    STAssertEqualObjects([@"this " : @"is " : @"string " : @"concatenation"],
     @"this is string concatenation", nil);
}

- (void)testVarArgConcatenation 
{
    NSString *concatenation = [@"a" concat:@"b", nil];
    STAssertEqualObjects(concatenation, @"ab", nil);

    concatenation = [concatenation concat:@"c", @"d", concatenation, nil];
    STAssertEqualObjects(concatenation, @"abcdab", nil);
}
37
votes

Use stringByAppendingString: this way:

NSString *string1, *string2, *result;

string1 = @"This is ";
string2 = @"my string.";

result = [result stringByAppendingString:string1];
result = [result stringByAppendingString:string2];

OR

result = [result stringByAppendingString:@"This is "];
result = [result stringByAppendingString:@"my string."];
31
votes

Macro:

// stringConcat(...)
//     A shortcut for concatenating strings (or objects' string representations).
//     Input: Any number of non-nil NSObjects.
//     Output: All arguments concatenated together into a single NSString.

#define stringConcat(...) \
    [@[__VA_ARGS__] componentsJoinedByString:@""]

Test Cases:

- (void)testStringConcat {
    NSString *actual;

    actual = stringConcat(); //might not make sense, but it's still a valid expression.
    STAssertEqualObjects(@"", actual, @"stringConcat");

    actual = stringConcat(@"A");
    STAssertEqualObjects(@"A", actual, @"stringConcat");

    actual = stringConcat(@"A", @"B");
    STAssertEqualObjects(@"AB", actual, @"stringConcat");

    actual = stringConcat(@"A", @"B", @"C");
    STAssertEqualObjects(@"ABC", actual, @"stringConcat");

    // works on all NSObjects (not just strings):
    actual = stringConcat(@1, @" ", @2, @" ", @3);
    STAssertEqualObjects(@"1 2 3", actual, @"stringConcat");
}

Alternate macro: (if you wanted to enforce a minimum number of arguments)

// stringConcat(...)
//     A shortcut for concatenating strings (or objects' string representations).
//     Input: Two or more non-nil NSObjects.
//     Output: All arguments concatenated together into a single NSString.

#define stringConcat(str1, str2, ...) \
    [@[ str1, str2, ##__VA_ARGS__] componentsJoinedByString:@""];
27
votes

When building requests for web services, I find doing something like the following is very easy and makes concatenation readable in Xcode:

NSString* postBody = {
    @"<?xml version=\"1.0\" encoding=\"utf-8\"?>"
    @"<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">"
    @" <soap:Body>"
    @"  <WebServiceMethod xmlns=\"\">"
    @"   <parameter>test</parameter>"
    @"  </WebServiceMethod>"
    @" </soap:Body>"
    @"</soap:Envelope>"
};
27
votes

Shortcut by creating AppendString (AS) macro ...

#define AS(A,B)    [(A) stringByAppendingString:(B)]
NSString *myString = @"This"; NSString *test = AS(myString,@" is just a test");

Note:

If using a macro, of course just do it with variadic arguments, see EthanB's answer.

13
votes
NSString *label1 = @"Process Name: ";
NSString *label2 = @"Process Id: ";
NSString *processName = [[NSProcessInfo processInfo] processName];
NSString *processID = [NSString stringWithFormat:@"%d", [[NSProcessInfo processInfo] processIdentifier]];
NSString *testConcat = [NSString stringWithFormat:@"%@ %@ %@ %@", label1, processName, label2, processID];
11
votes

Here's a simple way, using the new array literal syntax:

NSString * s = [@[@"one ", @"two ", @"three"] componentsJoinedByString:@""];
                  ^^^^^^^ create array ^^^^^
                                               ^^^^^^^ concatenate ^^^^^
9
votes
NSString *myString = @"This";
NSString *test = [myString stringByAppendingString:@" is just a test"];

After a couple of years now with Objective C I think this is the best way to work with Objective C to achieve what you are trying to achieve.

Start keying in "N" in your Xcode application and it autocompletes to "NSString". key in "str" and it autocompletes to "stringByAppendingString". So the keystrokes are quite limited.

Once you get the hang of hitting the "@" key and tabbing the process of writing readable code no longer becomes a problem. It is just a matter of adapting.

8
votes

The only way to make c = [a stringByAppendingString: b] any shorter is to use autocomplete at around the st point. The + operator is part of C, which doesn't know about Objective-C objects.

8
votes

How about shortening stringByAppendingString and use a #define:

#define and stringByAppendingString

Thus you would use:

NSString* myString = [@"Hello " and @"world"];

Problem is that it only works for two strings, you're required to wrap additional brackets for more appends:

NSString* myString = [[@"Hello" and: @" world"] and: @" again"];
8
votes
NSString *result=[NSString stringWithFormat:@"%@ %@", @"Hello", @"World"];
7
votes
NSString *label1 = @"Process Name: ";
NSString *label2 = @"Process Id: ";
NSString *processName = [[NSProcessInfo processInfo] processName];
NSString *processID = [NSString stringWithFormat:@"%d", [[NSProcessInfo processInfo] processIdentifier]];
NSString *testConcat = [NSString stringWithFormat:@"%@ %@ %@ %@", label1, processName, label2, processID];
6
votes

I tried this code. it's worked for me.

NSMutableString * myString=[[NSMutableString alloc]init];
myString=[myString stringByAppendingString:@"first value"];
myString=[myString stringByAppendingString:@"second string"];
6
votes

Was trying the following in the lldb pane

[NSString stringWithFormat:@"%@/%@/%@", three, two, one];

which errors.

instead use alloc and initWithFormat method:

[[NSString alloc] initWithFormat:@"%@/%@/%@", @"three", @"two", @"one"];
4
votes

This is for better logging, and logging only - based on dicius excellent multiple argument method. I define a Logger class, and call it like so:

[Logger log: @"foobar ", @" asdads ", theString, nil];

Almost good, except having to end the var args with "nil" but I suppose there's no way around that in Objective-C.

Logger.h

@interface Logger : NSObject {
}
+ (void) log: (id) first, ...;
@end

Logger.m

@implementation Logger

+ (void) log: (id) first, ...
{
    // TODO: make efficient; handle arguments other than strings
    // thanks to @diciu http://stackoverflow.com/questions/510269/how-do-i-concatenate-strings-in-objective-c
    NSString * result = @"";
    id eachArg;
    va_list alist;
    if(first)
    {
        result = [result stringByAppendingString:first];
        va_start(alist, first);
        while (eachArg = va_arg(alist, id)) 
        {
            result = [result stringByAppendingString:eachArg];
        }
        va_end(alist);
    }
    NSLog(@"%@", result);
}

@end 

In order to only concat strings, I'd define a Category on NSString and add a static (+) concatenate method to it that looks exactly like the log method above except it returns the string. It's on NSString because it's a string method, and it's static because you want to create a new string from 1-N strings, not call it on any one of the strings that are part of the append.

4
votes
NSNumber *lat = [NSNumber numberWithDouble:destinationMapView.camera.target.latitude];
NSNumber *lon = [NSNumber numberWithDouble:destinationMapView.camera.target.longitude];
NSString *DesconCatenated = [NSString stringWithFormat:@"%@|%@",lat,lon];
3
votes

Try stringWithFormat:

NSString *myString = [NSString stringWithFormat:@"%@ %@ %@ %d", "The", "Answer", "Is", 42];
3
votes

When dealing with strings often I find it easier to make the source file ObjC++, then I can concatenate std::strings using the second method shown in the question.

std::string stdstr = [nsstr UTF8String];

//easier to read and more portable string manipulation goes here...

NSString* nsstr = [NSString stringWithUTF8String:stdstr.c_str()];
3
votes

My preferred method is this:

NSString *firstString = @"foo";
NSString *secondString = @"bar";
NSString *thirdString = @"baz";

NSString *joinedString = [@[firstString, secondString, thirdString] join];

You can achieve it by adding the join method to NSArray with a category:

#import "NSArray+Join.h"
@implementation NSArray (Join)
-(NSString *)join
{
    return [self componentsJoinedByString:@""];
}
@end

@[] it's the short definition for NSArray, I think this is the fastest method to concatenate strings.

If you don't want to use the category, use directly the componentsJoinedByString: method:

NSString *joinedString = [@[firstString, secondString, thirdString] componentsJoinedByString:@""];
3
votes

You can use NSArray as

NSString *string1=@"This"

NSString *string2=@"is just"

NSString *string3=@"a test"  

NSArray *myStrings = [[NSArray alloc] initWithObjects:string1, string2, string3,nil];

NSString *fullLengthString = [myStrings componentsJoinedByString:@" "];

or

you can use

NSString *imageFullName=[NSString stringWithFormat:@"%@ %@ %@.", string1,string2,string3];
1
votes

Either of these formats work in XCode7 when I tested:

NSString *sTest1 = {@"This" " and that" " and one more"};
NSString *sTest2 = {
  @"This"
  " and that"
  " and one more"
};

NSLog(@"\n%@\n\n%@",sTest1,sTest2);

For some reason, you only need the @ operator character on the first string of the mix.

However, it doesn't work with variable insertion. For that, you can use this extremely simple solution with the exception of using a macro on "cat" instead of "and".

1
votes

For all Objective C lovers that need this in a UI-Test:

-(void) clearTextField:(XCUIElement*) textField{

    NSString* currentInput = (NSString*) textField.value;
    NSMutableString* deleteString = [NSMutableString new];

    for(int i = 0; i < currentInput.length; ++i) {
        [deleteString appendString: [NSString stringWithFormat:@"%c", 8]];
    }
    [textField typeText:deleteString];
}
0
votes
listOfCatalogIDs =[@[@"id[]=",listOfCatalogIDs] componentsJoinedByString:@""];
0
votes

Let's imagine that u don't know how many strings there.

NSMutableArray *arrForStrings = [[NSMutableArray alloc] init];
for (int i=0; i<[allMyStrings count]; i++) {
    NSString *str = [allMyStrings objectAtIndex:i];
    [arrForStrings addObject:str];
}
NSString *readyString = [[arrForStrings mutableCopy] componentsJoinedByString:@", "];
0
votes

Inspired by NSMutableString idea from Chris, I make a perfect macro imho. It supports insert nil elements without any Exceptions.

#import <libextobjc/metamacros.h>

#define STR_CONCAT(...) \
    ({ \
        __auto_type str__ = [NSMutableString string]; \
        metamacro_foreach_cxt(never_use_immediately_str_concatify_,, str__, __VA_ARGS__) \
        (NSString *)str__.copy; \
    })

#define never_use_immediately_str_concatify_(INDEX, CONTEXT, VAR) \
    [CONTEXT appendString:VAR ?: @""];

Example:

STR_CONCAT(@"button_bg_", @(count).stringValue, @".png"); 
// button_bg_2.png

If you like, you can use id type as parameter by using [VAR description] instead of NSString.