I'm trying to copy an NSString value out of an NSMutableArray into a new variable. NSString stringWithString is returning an NSString with the same memory address as the object in my array. Why?
#import <Foundation/Foundation.h>
int main(int argc, const char * argv[])
{
#autoreleasepool {
NSMutableArray *arr = [NSMutableArray arrayWithObject:#"first"];
NSLog(#"string is '%#' %p", [arr objectAtIndex:0], [arr objectAtIndex:0]);
// copy the string
NSString *copy = [NSString stringWithString:[arr objectAtIndex:0]];
NSLog(#"string is '%#' %p", copy, copy);
}
return 0;
}
1) Whenever you're creating a string using the #"" syntax, the framework will automatically cache the string. NSString is a very special class, but the framework will take care of it. When you use #"Some String" in multiple places of your app, they will all point to the same address in memory. Only when you're using something like -initWithData:encoding, the string won't be cached.
2) The other answers suggested that you should use -copy instead, but -copy will only create a copy of the object if the object is mutable. (like NSMutableString)
When you're sending -copy to an immutable object (like NSString), it'll be the same as sending it -retain which returns the object itself.
NSString *originalString = #"Some String";
NSString *copy = [originalString copy];
NSString *mutableCopy1 = [originalString mutableCopy];
NSString *mutableCopy2 = [mutableCopy copy];
NSString *anotherString = [[NSString alloc] initWithString:originalString];
--> originalString, copy, mutableCopy2 and anotherString will all point to the same memory address, only mutableCopy1 points do a different region of memory.
Since NSString instances are not mutable, the +stringWithString: method is simply returning the input string with an incremented reference count.
If you really want to force the creating of a new, identical string, try:
NSString * copy = [NSString stringWithFormat:#"%#", [arr objectAtIndex:0]];
There is little point in doing so, though, unless you need the pointer to be unique for some other reason...
I have made a program that gets some strings in input from the user (it stops typing "exit"), puts them in a NSMutableArray and sort them:
#import <Foundation/Foundation.h>
#import <Cocoa/Cocoa.h>
NSInteger compare( id id1, id id2, void* context)
{
NSString* str1=[id1 stringValue], *str2=[id2 stringValue]; /* ****** exception here */
const char* buf1, *buf2;
buf1=[str1 UTF8String];
buf2=[str2 UTF8String];
if(strcmp(buf1,buf2)<0)
return NSOrderedAscending;
else
return NSOrderedDescending;
}
int main (int argc, const char * argv[])
{
NSAutoreleasePool* pool=[[NSAutoreleasePool alloc]init];
NSMutableArray* array=[[NSMutableArray alloc]init];
NSString* str=#"";
char buffer[100];
NSLog(#"Type a sequence of strings, ending with 'exit', the strings will be sorted in alphabethical order");
while(! [str isEqualToString:#"exit\n"])
{
fgets(buffer,100,stdin);
str=[NSString stringWithUTF8String: buffer];
[array addObject: str];
}
[array sortUsingFunction: compare context: NULL];
[array release];
[pool drain];
return 0;
}
But I get an exception in the line that I have marked with "**", it says:
2012-05-09 00:10:14.502 CLITest[1029:903] -[NSCFString stringValue]: unrecognized selector sent to instance 0x10010cbf0
It seems like it doesn't take the string value from the id.Why? How should I change the comparator method?
id1 and id2 are actually NSStrings, even if they are casted to id and passed to your function (this approach is useful because you can define your compare function in order to sort custom objects).
It doesn't make sense to call stringValue on a string (and, in fact, NSString do not have a member function named stringValue).
To work with strings just cast back to NSStrings.
NSString *s1 = (NSString*) id1;
NSString *s2 = (NSString*) id2;
This is not strictly necessary (you can even work directly with id1 and id2) but casting will avoid you to get compiler warnings (also it's a clearer code).
Ideally, I would like to make a function add objects in a NSMutableArray, and then do whatever I want with this array in another function.
Here is what I've tried to do lately, of course it doesn't work but it gives you an idea of what I want to do:
- (void)someThing
{
(...)
NSMutableArray *arrayOfThings = [[NSMutableArray alloc] init];
while (theObject = [aNSEnumerator nextObject]) {
const char *theObject_fixed = [theObject UTF8String];
function_something(theObject_fixed);
}
// do something with arrayOfThings
}
void function_something(const char *file)
{
(...)
unsigned int *p = memmem(buffer, fileLen, bytes, 4);
NSMutableString *aString = [[NSMutableString alloc] initWithCapacity:48];
unsigned long off_to_string = 0x10 + 4 + ((void *)p) - ((void *)buffer);
for (unsigned long c = off_to_string; c<off_to_string+0x30; c++)
{
[aString appendFormat:#"%.2x", (int)buffer[c]];
}
NSLog(#"%s: %#", file, aString);
[arrayOfThings addObject:[aString copy]];
free(buffer);
There are two ways to go about this:
The first requires only a slight modification to your code will allow you to do what you want:
In the funciton someThing pass the mutable array as an additional parameter.
function_something(theObject_fixed, arrayOfThings);
Then change function_something to accept that parameter.
void function_something(const char *file, NSMutableArray *arrayOfThings) {
// Code remains the same
}
The other and in my opinion better solution would be for the function_something to return the fixed string as an NSString object and let someThing do the adding to the mutable array.
So we get something like this in someThing:
...
NSString *aString = function_something(theObject_fixed);
[arrayOfThings addObject:aString];
And then a redefined *function_something*:
NSString* function_something(const char *file) {
...
return [aString autorelease];
}
By the way, your code is leaking memory. Be careful with you retain/release/autorelease.
I want to print values of all the types like char, long... so on and also nsdate, nsdictionary, frame ....I want to now to print values of each type variables.
Primitive types such as int, float, double, etc can be printed in the same fashion they are printed in C, using printf, fprintf, etc. If you need to print the data of a class you can often use NSObject's method (NSString *)description to get a NSString representing the data of the object. Here is an example...
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
NSString *string = [NSString stringWithFormat:#"Hello World!"];
NSDate *date = [NSDate dateWithTimeIntervalSinceNow:0];
NSArray *array = [NSArray arrayWithObject:#"Hello There!"];
char *c_string = "Familiar ol' c string!";
int number = 3;
printf("C String: %s\n",c_string);
printf("Int number: %u\n", number);
//In 10.5+ do not use [NSString cString] as it has been deprecated
printf("NSString: %s\n", [string UTF8String]);
printf("NSDate: %s\n", [date.description UTF8String]);
printf("NSArray: %s\n", [array.description UTF8String]);
//If you are using this information for debugging, it's often useful to pass the object to NSLOG()
NSLog(#"NSArray *array = \n%#", array);
[pool drain];
return 0;
}
Edit: I thought it would helpful to see the output when the example is ran...
C String: Familiar ol' c string!
Int number: 3
NSString: Hello World!
NSDate: 2010-03-12 01:52:31 -0600
NSArray: (
"Hello There!"
)
2010-03-12 01:52:31.385 printfTest[2828:a0f] NSArray *array =
(
"Hello There!"
)
Is there any way to create a new
NSString from a format string like #"xxx=%#, yyy=%#" and a NSArray of objects?
In the NSSTring class there are many methods like:
- (id)initWithFormat:(NSString *)format arguments:(va_list)argList
- (id)initWithFormat:(NSString *)format locale:(id)locale arguments:(va_list)argList
+ (id)stringWithFormat:(NSString *)format, ...
but non of them takes a NSArray as an argument, and I cannot find a way to create a va_list from a NSArray...
It is actually not hard to create a va_list from an NSArray. See Matt Gallagher's excellent article on the subject.
Here is an NSString category to do what you want:
#interface NSString (NSArrayFormatExtension)
+ (id)stringWithFormat:(NSString *)format array:(NSArray*) arguments;
#end
#implementation NSString (NSArrayFormatExtension)
+ (id)stringWithFormat:(NSString *)format array:(NSArray*) arguments
{
char *argList = (char *)malloc(sizeof(NSString *) * arguments.count);
[arguments getObjects:(id *)argList];
NSString* result = [[[NSString alloc] initWithFormat:format arguments:argList] autorelease];
free(argList);
return result;
}
#end
Then:
NSString* s = [NSString stringWithFormat:#"xxx=%#, yyy=%#" array:#[#"XXX", #"YYY"]];
NSLog( #"%#", s );
Unfortunately, for 64-bit, the va_list format has changed, so the above code no longer works. And probably should not be used anyway given it depends on the format that is clearly subject to change. Given there is no really robust way to create a va_list, a better solution is to simply limit the number of arguments to a reasonable maximum (say 10) and then call stringWithFormat with the first 10 arguments, something like this:
+ (id)stringWithFormat:(NSString *)format array:(NSArray*) arguments
{
if ( arguments.count > 10 ) {
#throw [NSException exceptionWithName:NSRangeException reason:#"Maximum of 10 arguments allowed" userInfo:#{#"collection": arguments}];
}
NSArray* a = [arguments arrayByAddingObjectsFromArray:#[#"X",#"X",#"X",#"X",#"X",#"X",#"X",#"X",#"X",#"X"]];
return [NSString stringWithFormat:format, a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9] ];
}
Based on this answer using Automatic Reference Counting (ARC): https://stackoverflow.com/a/8217755/881197
Add a category to NSString with the following method:
+ (id)stringWithFormat:(NSString *)format array:(NSArray *)arguments
{
NSRange range = NSMakeRange(0, [arguments count]);
NSMutableData *data = [NSMutableData dataWithLength:sizeof(id) * [arguments count]];
[arguments getObjects:(__unsafe_unretained id *)data.mutableBytes range:range];
NSString *result = [[NSString alloc] initWithFormat:format arguments:data.mutableBytes];
return result;
}
One solution that came to my mind is that I could create a method that works with a fixed large number of arguments like:
+ (NSString *) stringWithFormat: (NSString *) format arguments: (NSArray *) arguments {
return [NSString stringWithFormat: format ,
(arguments.count>0) ? [arguments objectAtIndex: 0]: nil,
(arguments.count>1) ? [arguments objectAtIndex: 1]: nil,
(arguments.count>2) ? [arguments objectAtIndex: 2]: nil,
...
(arguments.count>20) ? [arguments objectAtIndex: 20]: nil];
}
I could also add a check to see if the format string has more than 21 '%' characters and throw an exception in that case.
#Chuck is correct about the fact that you can't convert an NSArray into varargs. However, I don't recommend searching for the pattern %# in the string and replacing it each time. (Replacing characters in the middle of a string is generally quite inefficient, and not a good idea if you can accomplish the same thing in a different way.) Here is a more efficient way to create a string with the format you're describing:
NSArray *array = ...
NSAutoreleasePool *pool = [NSAutoreleasePool new];
NSMutableArray *newArray = [NSMutableArray arrayWithCapacity:[array count]];
for (id object in array) {
[newArray addObject:[NSString stringWithFormat:#"x=%#", [object description]]];
}
NSString *composedString = [[newArray componentsJoinedByString:#", "] retain];
[pool drain];
I included the autorelease pool for good housekeeping, since an autoreleased string will be created for each array entry, and the mutable array is autoreleased as well. You could easily make this into a method/function and return composedString without retaining it, and handle the autorelease elsewhere in the code if desired.
This answer is buggy. As noted, there is no solution to this problem that is guaranteed to work when new platforms are introduced other than using the "10 element array" method.
The answer by solidsun was working well, until I went to compile with 64-bit architecture. This caused an error:
EXC_BAD_ADDRESS type EXC_I386_GPFLT
The solution was to use a slightly different approach for passing the argument list to the method:
+ (id)stringWithFormat:(NSString *)format array:(NSArray*) arguments;
{
__unsafe_unretained id * argList = (__unsafe_unretained id *) calloc(1UL, sizeof(id) * arguments.count);
for (NSInteger i = 0; i < arguments.count; i++) {
argList[i] = arguments[i];
}
NSString* result = [[NSString alloc] initWithFormat:format, *argList] ;// arguments:(void *) argList];
free (argList);
return result;
}
This only works for arrays with a single element
There is no general way to pass an array to a function or method that uses varargs. In this particular case, however, you could fake it by using something like:
for (NSString *currentReplacement in array)
[string stringByReplacingCharactersInRange:[string rangeOfString:#"%#"]
withString:currentReplacement];
EDIT: The accepted answer claims there is a way to do this, but regardless of how fragile this answer might seem, that approach is far more fragile. It relies on implementation-defined behavior (specifically, the structure of a va_list) that is not guaranteed to remain the same. I maintain that my answer is correct and my proposed solution is less fragile since it only relies on defined features of the language and frameworks.
For those who need a Swift solution, here is an extension to do this in Swift
extension String {
static func stringWithFormat(format: String, argumentsArray: Array<AnyObject>) -> String {
let arguments = argumentsArray.map { $0 as! CVarArgType }
let result = String(format:format, arguments:arguments)
return result
}
}
Yes, it is possible. In GCC targeting Mac OS X, at least, va_list is simply a C array, so you'll make one of ids, then tell the NSArray to fill it:
NSArray *argsArray = [[NSProcessInfo processInfo] arguments];
va_list args = malloc(sizeof(id) * [argsArray count]);
NSAssert1(args != nil, #"Couldn't allocate array for %u arguments", [argsArray count]);
[argsArray getObjects:(id *)args];
//Example: NSLogv is the version of NSLog that takes a va_list instead of separate arguments.
NSString *formatSpecifier = #"\n%#";
NSString *format = [#"Arguments:" stringByAppendingString:[formatSpecifier stringByPaddingToLength:[argsArray count] * 3U withString:formatSpecifier startingAtIndex:0U]];
NSLogv(format, args);
free(args);
You shouldn't rely on this nature in code that should be portable. iPhone developers, this is one thing you should definitely test on the device.
- (NSString *)stringWithFormat:(NSString *)format andArguments:(NSArray *)arguments {
NSMutableString *result = [NSMutableString new];
NSArray *components = format ? [format componentsSeparatedByString:#"%#"] : #[#""];
NSUInteger argumentsCount = [arguments count];
NSUInteger componentsCount = [components count] - 1;
NSUInteger iterationCount = argumentsCount < componentsCount ? argumentsCount : componentsCount;
for (NSUInteger i = 0; i < iterationCount; i++) {
[result appendFormat:#"%#%#", components[i], arguments[i]];
}
[result appendString:[components lastObject]];
return iterationCount == 0 ? [result stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]] : result;
}
Tested with format and arguments:
NSString *format = #"xxx=%#, yyy=%# last component";
NSArray *arguments = #[#"XXX", #"YYY", #"ZZZ"];
Result: xxx=XXX, yyy=YYY last component
NSString *format = #"xxx=%#, yyy=%# last component";
NSArray *arguments = #[#"XXX", #"YYY"];
Result: xxx=XXX, yyy=YYY last component
NSString *format = #"xxx=%#, yyy=%# last component";
NSArray *arguments = #[#"XXX"];
Result: xxx=XXX last component
NSString *format = #"xxx=%#, yyy=%# last component";
NSArray *arguments = #[];
Result: last component
NSString *format = #"some text";
NSArray *arguments = #[#"XXX", #"YYY", #"ZZZ"];
Result: some text
I found some code on the web that claims that this is possible however I haven't managed to do it myself, however if you don't know the number of arguments in advance you also need to build the format string dynamically so I just don't see the point.
You better off just building the string by iterating the array.
You might find the stringByAppendingString: or stringByAppendingFormat: instance method handy .
One can create a category for NSString and make a function which receives a format, an array and returns the string with replaced objects.
#interface NSString (NSArrayFormat)
+ (NSString *)stringWithFormat:(NSString *)format arrayArguments:(NSArray *)arrayArguments;
#end
#implementation NSString (NSArrayFormat)
+ (NSString *)stringWithFormat:(NSString *)format arrayArguments:(NSArray *)arrayArguments {
static NSString *objectSpecifier = #"%#"; // static is redundant because compiler will optimize this string to have same address
NSMutableString *string = [[NSMutableString alloc] init]; // here we'll create the string
NSRange searchRange = NSMakeRange(0, [format length]);
NSRange rangeOfPlaceholder = NSMakeRange(NSNotFound, 0); // variables are declared here because they're needed for NSAsserts
NSUInteger index;
for (index = 0; index < [arrayArguments count]; ++index) {
rangeOfPlaceholder = [format rangeOfString:objectSpecifier options:0 range:searchRange]; // find next object specifier
if (rangeOfPlaceholder.location != NSNotFound) { // if we found one
NSRange substringRange = NSMakeRange(searchRange.location, rangeOfPlaceholder.location - searchRange.location);
NSString *formatSubstring = [format substringWithRange:substringRange];
[string appendString:formatSubstring]; // copy the format from previous specifier up to this one
NSObject *object = [arrayArguments objectAtIndex:index];
NSString *objectDescription = [object description]; // convert object into string
[string appendString:objectDescription];
searchRange.location = rangeOfPlaceholder.location + [objectSpecifier length]; // update the search range in order to minimize search
searchRange.length = [format length] - searchRange.location;
} else {
break;
}
}
if (rangeOfPlaceholder.location != NSNotFound) { // we need to check if format still specifiers
rangeOfPlaceholder = [format rangeOfString:#"%#" options:0 range:searchRange];
}
NSAssert(rangeOfPlaceholder.location == NSNotFound, #"arrayArguments doesn't have enough objects to fill specified format");
NSAssert(index == [arrayArguments count], #"Objects starting with index %lu from arrayArguments have been ignored because there aren't enough object specifiers!", index);
return string;
}
#end
Because NSArray is created at runtime we cannot provide compile-time warnings, but we can use NSAssert to tell us if number of specifiers is equal with number of objects within array.
Created a project on Github where this category can be found. Also added Chuck's version by using 'stringByReplacingCharactersInRange:' plus some tests.
Using one million objects into array, version with 'stringByReplacingCharactersInRange:' doesn't scale very well (waited about 2 minutes then closed the app). Using the version with NSMutableString, function made the string in about 4 seconds. The tests were made using simulator. Before usage, tests should be done on a real device (use a device with lowest specs).
Edit: On iPhone 5s the version with NSMutableString takes 10.471655s (one million objects); on iPhone 5 takes 21.304876s.
Here's the answer without explicitly creating an array:
NSString *formattedString = [NSString stringWithFormat:#"%# World, Nice %#", #"Hello", #"Day"];
First String is the target string to be formatted, the next string are the string to be inserted in the target.
No, you won't be able to. Variable argument calls are solved at compile time, and your NSArray has contents only at runtime.