What's the correct way to print an NSString in Objective-C? A lot of examples use NSLog(), but according to the documentation:
NSLog is a FoundationKit function for printing debug statements to the console.
...
NSLog works basically like:
fprintf(stderr, format_string, args ...);
Which to me is a bit like the _TRACE macro in Win32/C++. I don't want to print to stderr, I want to print to stdout. There are people who suggest using printf() as follows:
printf("%s", [str cStringUsingEncoding:NSUTF8StringEncoding]);
But this seems like an extra level on indirection to get the NSString printed, and it doesn't "feel" like the solution.
Spewing stuff to stdout is actually a pretty rare thing to do in Cocoa, given that almost all projects are GUI in nature. There are relatively few projects that are built as command line tools or otherwise need to deal with stdout.
However, the Foundation does provide the means to write to stdout. Specifically, NSFileHandle has fileHandleWithStandardOutput which gives you a file handle that can write to stdout.
From there, it is a matter of converting the NSString to an NSData and writing it.
Quite a few steps, but easily wrapped up in a reusable function:
void MyLog(NSString *format, ...) {
va_list args;
va_start(args, format);
NSString *formattedString = [[NSString alloc] initWithFormat: format
arguments: args];
va_end(args);
[[NSFileHandle fileHandleWithStandardOutput]
writeData: [formattedString dataUsingEncoding: NSNEXTSTEPStringEncoding]];
[formattedString release];
}
Well this is the solution.
Since printf is a pure C function, it won't recognize the Objective-C objects. (NSLog's formatter is distinct from printf's one.) Therefore, you have to convert it into a C string before formatting.
BTW you can use [str UTF8String] instead of [str cStringUsingEncoding:NSUTF8StringEncoding].
C string (UTF8String) is a pointer to a structure inside the string object.
NSString *str = #"Hello, World.";
printf("%s\n", [str UTF8String]);
I think you'll find these adequate for your needs:
// print to stdout
static void NSPrint(NSString *format, ...) {
va_list args;
va_start(args, format);
NSString *string = [[NSString alloc] initWithFormat:format arguments:args];
va_end(args);
fprintf(stdout, "%s\n", [string UTF8String]);
#if !__has_feature(objc_arc)
[string release];
#endif
}
// print to stderr
static void NSPrintErr(NSString *format, ...) {
va_list args;
va_start(args, format);
NSString *string = [[NSString alloc] initWithFormat:format arguments:args];
va_end(args);
fprintf(stderr, "%s\n", [string UTF8String]);
#if !__has_feature(objc_arc)
[string release];
#endif
}
You should use the custom file handler or write a macro yourself.
Tip: when NSLog prints out an object it uses object's debugDescription method. You could override this method for your custom NSObject subclasses to print custom debugInfo to stdout.
I just do:
define NSPrintf(...) printf( "%s", [[NSString stringWithFormat: __VA_ARGS__] UTF8String] )
Then i can use it as:
NSPrintf( #"Sorry %#, I can't do that\n", name );
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";
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;
}
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.
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.
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];
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.
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);
}
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."];
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:#""];
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>"
};
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.
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];
Here's a simple way, using the new array literal syntax:
NSString * s = [#[#"one ", #"two ", #"three"] componentsJoinedByString:#""];
^^^^^^^ create array ^^^^^
^^^^^^^ concatenate ^^^^^
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.
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.
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"];
NSString *result=[NSString stringWithFormat:#"%# %#", #"Hello", #"World"];
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];
I tried this code. it's worked for me.
NSMutableString * myString=[[NSMutableString alloc]init];
myString=[myString stringByAppendingString:#"first value"];
myString=[myString stringByAppendingString:#"second string"];
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"];
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.
NSNumber *lat = [NSNumber numberWithDouble:destinationMapView.camera.target.latitude];
NSNumber *lon = [NSNumber numberWithDouble:destinationMapView.camera.target.longitude];
NSString *DesconCatenated = [NSString stringWithFormat:#"%#|%#",lat,lon];
Try stringWithFormat:
NSString *myString = [NSString stringWithFormat:#"%# %# %# %d", "The", "Answer", "Is", 42];
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()];
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:#""];
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];
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".
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];
}
listOfCatalogIDs =[#[#"id[]=",listOfCatalogIDs] componentsJoinedByString:#""];
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:#", "];
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.