I have the following method:
(void)makeString:(NSString *)str1,... {
va_list strings;
NSString *innerText = [[NSString alloc] init];
NSString *tmpStr = [[NSString alloc] init];
if (str1) {
va_start(strings, str1);
while (tmpStr = va_arg(strings, id)) {
innerText = [innerText stringByAppendingString:tmpStr];
}
label.text = [str1 stringByAppendingString:innerText];
}
[tmpStr release];
}
I will eventually get to Objective C Memory Management reading, where I'm sure I will find the answer to this - probably related to pointers and copying - , but for now, can anyone explain why if I add [innerText release]; as the last line of this function, i get an EXC_BAD_ACCESS error at runtime?
First, your code is erroneous.
As far as I can see you are only concatenating the strings to assign the result to label.text.
I assume that label is an ivar, so label.text = … ist legal. Then the following should do it:
- (void)makeString: (NSString *)str1, ...
{
if (str1) {
NSString *tmpStr;
va_list strings;
va_start(strings, str1);
while (tmpStr = va_arg(strings, id)) {
str1 = [str1 stringByAppendingString: tmpStr];
}
label.text = str1;
}
}
Some notes:
You should not release any input parameter unless your method is about releasing something.
As the first answer stated, you should not release the result of stringByAppendingString: unless
you have retained it before.
[Update]
I changed the answer because it contained an error. label.text = str1 should retain str1 of course (if it wants to keep it). Especially the calling code should not retain str1 unless it wants to keep it for itself.
stringByAppendingString returns an autoreleased string, which is replacing your original assignment. So your release is not needed. But you are leaking memory with the two allocs above.
You should probably use [NSString initWithCString:va_arg(strings, id)] to assign the tmpStr too.
Related
Suppose I have a function
- (NSString *)fullNameCopy {
return [[NSString alloc] initWithFormat:#"%# %#", self.firstName, self.LastName];
}
Can somebody tell me how to call this function, how to assign its value to a new object, and how then to release it, avoiding memory leaks, and bad access.
Would it be like
NSSting *abc = [object fullNameCopy];
// Use it and release
[abc release];
or I should alloc abc string too ?
Update:
The point here, Can I return non-autorelease objects from a function and then release them in the calling function. As per Obj-C function naming conventions, a function name containing alloc or copy should return object assuming that calling function has the ownership.
As in above case, my function "fullNameCopy" return a non-autoreleased abject, and I want to release them in the calling function.
You are right. Since the method name contains the word ‘copy’, Cocoa convention dictates that the method returns an object that is owned by the caller. Since the caller owns that object, it is responsible for releasing it. For example:
- (void)someMethod {
NSString *abc = [object fullNameCopy];
// do something with abc
[abc release];
}
Alternatively, you could use -autorelease instead of -release:
- (void)someMethod {
NSString *abc = [[object fullNameCopy] autorelease];
// do something with abc
}
Refer this post
UPDATE:
- (NSString *)fullNameCopy {
NSString *returnString = [NSString stringWithFormat:#"%# %#", self.firstName, self.LastName]; // Autorelease object.
return returnString;
}
-(void) someFunction {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
NSString *fullName = [self fullNameCopy];
[pool release]
}
Like This:
- (NSString *)fullName {
NSString * retVal = [[NSString alloc] initWithFormat:#"%# %#", self.firstName, self.LastName];
return [retVal autoRelease];
}
Then
NSSting *abc = [object fullName];
return [[[NSString alloc] initWithFormat:#"%# %#", self.firstName, self.LastName]autorelease];
I post this question again but with more precision this time,
first, I have this function who return a string, there is some error about memory management or this fonction is ok?
-(NSString *) motAvecCle:(NSString *) cle
{
NSString *motRetour;
motRetour = #"";
cle = [FonctionUtile concatener:[[tableauConfig singletonTableauConfig] langueAffichage] chaine2:#"_" chaine3:[FonctionUtile trim:[cle uppercaseString]] chaine4:#""];
motRetour = [FonctionUtile trim:[dictionnaireLangue objectForKey:cle]];
if (motRetour == nil) {
motRetour = #"Erreur";
}
return motRetour;
}
and when I call this fonction,
NSString *myString = #"";
myString = [self motAvecCle:#"fr"]; // I must do this?
myString = [[self motAvecCle:#"en"]retain]; //or do this?
thx again...
The method motAvecCle: returns an object you do not own. Therefore, at some point it is going to disappear. Whether you care or not depends on where myString is defined. If it's in the same scope:
-(void) foo
{
NSString *myString = [self motAvecCle:#"fr"];
// do some stuff
}
you do not want to retain it (except in one circumstance) because the reference will disappear when foo exits which means if you had retained it you'd need to release it again first.
The one circumstance for retaining is if you modify the object you got the string from i.e. self in this case. That might cause the string to go away (although probably not in your specific example).
If myString is an instance variable of the object, you do want to retain it because otherwise it will disappear (possibly) the next time the auto release pool is drained. However, before assigning the instance variable, you must be sure to release the old value of the instance variable, unless it's actually the same string you are assigning i.e. you need to do something like this:
-(void) foo
{
NSString *tmp = [[self motAvecCle:#"fr"] retain]; // it's a string, technically you should copy, not retain
[myString release];
myString = tmp;
// do some stuff
}
Since you'd have to do that every time you want to assign the ivar, it's normal to create an accessor e.g.
-(void) setMyString: (NSString*) newValue
{
NSString* tmp = [newValue copy];
[myString release];
myString = tmp;
}
-(void) foo
{
[self setMyString: [self motAvecCle:#"fr"]];
// do some stuff
}
If you use properties, you can use #synthesize to create the accessors.
Im just wrapping up my app, so im onto the stage of running instruments to identify leaks in the app. Ive come across a leak that I cannot work out why it is being registered as a leak.
I have the following lines for example:
NSString *imageType = [[[NSString alloc] initWithString:[loopString substringToIndex:[loopString rangeOfString:#"</IMAGE>"].location]] autorelease];
imageType = [imageType substringFromIndex:[imageType rangeOfString:#"<IMAGE>"].location + :#"<IMAGE>".length];
So basically all im doing is pulling out a section of the "loopstring" and putting that into the imagetype string than just cutting off the trailing fluff of the string using the SubstringFromIndex method.
When I run instruments it says "NSCFString substringwithRange" leak. It highlights the second line:
imageType = [imageType substringFromIndex:[imageType rangeOfString:#"<IMAGE>"].location + :#"<IMAGE>".length];
I would think the substringFromIndex method should return a string that is automatically added to the autorelease pool.
Any ideas on where im going wrong?
Thanks
Following is the refactored code:
- (void)SetupTop10:(NSString *)Top10Data
{
while (Top10Data != #"") {
NSLog(Top10Data);
if ([Top10Data rangeOfString:#"</TOP10ENTRY>"].location == NSNotFound){
Top10Data = #"";
}
else
{
NSString *loopString = [Top10Data substringToIndex:[Top10Data rangeOfString:#"</TOP10ENTRY>"].location + 13];
Top10Data = [Top10Data stringByReplacingOccurrencesOfString:loopString withString:#""];
//NOW CREATE A RECORD FOR THIS ITEM
NSString *imageType = [loopString substringToIndex:[loopString rangeOfString:#"</IMAGE>"].location];
imageType = [imageType substringFromIndex:[imageType rangeOfString:#"<IMAGE>"].location + 7];
NSString *displayText = [loopString substringToIndex:[loopString rangeOfString:#"</DISPLAYTEXT>"].location];
displayText = [displayText substringFromIndex:[displayText rangeOfString:#"<DISPLAYTEXT>"].location + 13];
NSString *link = [loopString substringToIndex:[loopString rangeOfString:#"</INTERESTID>"].location];
link = [link substringFromIndex:[link rangeOfString:#"<INTERESTID>"].location + 12];
[Top10Images addObject:imageType];
[Top10Links addObject:link];
[Top10s addObject:displayText];
Top10RowCount = Top10RowCount + 1;
}
}
[self.Top10Table reloadData];
Top10Table.hidden = NO;
loadingLabel.hidden = YES;
loadingIndicator.hidden = YES;
}
//******************
It doesn't look leaky. But why
NSString *imageType = [[[NSString alloc] initWithString:
[loopString substringToIndex:[loopString
rangeOfString:#"</IMAGE>"].location]
] autorelease];
if you effectively get the same with
NSString *imageType = [loopString substringToIndex:[loopString
rangeOfString:#"</IMAGE>"].location];
with half the memory usage?
Leaks will tell you where the leaked memory was allocated. If you click around (there's a right-arrow icon by the memory address, I think) then you can look at all the allocations/retains/releases for that addresses.
In this example, Leaks will point you to the first line, when it's the fifth one that "leaks" (actually it's a missing release in dealloc/on assignment that leaks):
NSString * s = [someString substringFromIndex:1];
[myArray addObject:s];
// ...
NSString * s2 = [myArray lastObject];
instanceVariable = [s2 retain];
// ... and forget to release in dealloc
What does tableView:cellForRowAtIndexPath: do?
I can't see any problem in the above code. Did you release Top10Images in your dealloc method?
I'm trying to include the elements of an array in the NSString that's returned by the -description method in my class. No clue how to do this in Objective-C...in Java there's string concatenation or StringBuilder, what's the equivalent in Obj-C?
TIA..
Just use NSArray's componentsJoinedByString: method with whatever you want between them as the argument.
NSString *elementsSquishedTogether = [myArray componentsJoinedByString:#""];
NSString *connectedByACommaAndSpace = [myArray componentsJoinedByString:#", "];
If you have a C array, you can turn it into an NSArray with NSArray *converted = [NSArray arrayWithObjects:yourCArray count:yourArrayCount].
The title of your thread talks about C arrays, so here's a modification of jsumners' answer that will deal wiith C arrays.
myArray is assumed to be an ivar declared thusly:
int* myArray;
storage for myArray is assumed to be malloc'd at some point and the size of it is in an ivar declared:
int myArraySize;
The code for description goes something like
- (NSString *)description
{
NSMutableString *returnString = [[[NSMutableString alloc] init] autorelease];
for (int i = 0 ; i < myArraySize ; i++)
{
if (i > 0)
{
[returnString appendString: #", "];
}
[returnString appendFormat: #"%d", myArray[i]];
}
return [NSString stringWithFormat: #"[%#]", returnString];
}
There are variations. The above version formats the string with bracket delimiters and commas between elements. Also, it returns an NSString instead of an NSMutableString which is not a big deal, but I feel that if you say you are returning an immutable object, you probably should.
The following could should "build" a string representation of your array. Notice that it is using the -description method of the objects in the array. If you want something different you will have to make the necessary change.
- (NSString *)description: (id) myArr {
NSMutableString *returnString = [[[NSMutableString alloc] init] autorelease];
for (int i = 0, j = [myaArr count]; i < j; i++) {
[returnString appendString: [[myArr objectAtIndex: i] description]];
}
return [NSString stringWithString: returnString];
}
Edit:
As JeremyP said, I answered this using Objective-C arrays. I guess I just forgot the question when I started writing my code. I'm going to leave my answer as an alternative way to do it, though. I've also fixed the return string type from a mutable string to an immutable string (as it should be).
I want to call a method which returns two values
basically lets say my method is like the below (want to return 2 values)
NSString* myfunc
{
NSString *myString = #"MYDATA";
NSString *myString2 = #"MYDATA2";
return myString;
return myString2;
}
So when i call it, i would use??
NSString* Value1 = [self myfunc:mystring];
NSString* Value2 = [self myfunc:mystring2];
I guess im doing something wrong with it, can anyone help me out?
Thanks
You can only return 1 value. That value can be a struct or an object or a simple type. If you return a struct or object it can contain multiple values.
The other way to return multiple values is with out parameters. Pass by reference or pointer in C.
Here is a code snippet showing how you could return a struct containing two NSStrings:
typedef struct {
NSString* str1;
NSString* str2;
} TwoStrings;
TwoStrings myfunc(void) {
TwoStrings result;
result.str1 = #"data";
result.str2 = #"more";
return result;
}
And call it like this:
TwoStrings twoStrs = myfunc();
NSLog(#"str1 = %#, str2 = %#", twoStrs.str1, twoStrs.str2);
You need to be careful with memory management when returning pointers even if they are wrapped inside a struct. In Objective-C the convention is that functions return autoreleased objects (unless the method name starts with create/new/alloc/copy).
You have a few options:
NSArray: Just return an array. Pretty simple.
Pointers: Pass in two pointers, and write to them instead of returning anything. Make sure to check for NULL!
Structure: Create a struct that has two fields, one for each thing you want to return, and return one of that struct.
Object: Same a structure, but create a full NSObject subclass.
NSDictionary: Similar to NSArray, but removes the need to use magic ordering of the values.
As you can only return one value/object, maybe wrap them up in an array:
-(NSArray*) arrayFromMyFunc
{
NSString *myString = #"MYDATA";
NSString *myString2 = #"MYDATA2";
return [NSArray arrayWithObjects:myString,myString2,nil];
}
You can then use it like this:
NSArray *arr = [self arrayFromMyFunc];
NSString *value1 = [arr objectAtIndex:0];
NSString *value2 = [arr objectAtIndex:1];
You could pass results back by reference, but this is easy to get wrong (syntactically, semantically, and from memory management point of view).
Edit One more thing: Make sure that you really need two return values. If they are quite independent, two separate function are often the better choice - better reusabilty and mentainable. Just in case you are making this as a matter of premature optimization. :-)
You can only directly return one value from a function. But there is a way of doing it.
-(void) myfuncWithVal1:(NSString**)val1 andVal2:(NSString**)val2
{
*val1 = #"MYDATA";
*val2 = #"MYDATA2";
}
Then to call it outside the method you'd use:
NSString* a;
NSString* b;
[self myfuncWithVal1:&a andVal2:&b];
void myfunc(NSString **string1, NSString **string2)
{
*string1 = #"MYDATA";
*string2 = #"MYDATA2";
}
...
NSString *value1, *value2;
myfunc(&value1, &value2);
Remember that you need to pass a pointer to a pointer when working with strings and other objects.
Wrap the two strings in an NSArray:
- (NSArray*)myFunc
{
NSString *myString = #"MYDATA";
NSString *myString2 = #"MYDATA2";
return [NSArray arrayWithObjects:myString, myString2, nil];
}
NSArray *theArray = [self myFunc]
NSString *value1 = [theArray objectAtIndex:0];
NSString *value2 = [theArray] objectAtIndex:1];
I see everyone has mentioned an NSArray but I'd go with an NSDictionary so the values don't have to be added in order or even at all. This means it is able to handle a situation where you only want to return the second string.
- (NSDictionary*)myFunction {
NSString *myString1 = #"string1";
NSString *myString2 = #"string2";
return [NSDictionary dictionaryWithObjectsAndKeys: myString1, #"key1", myString2, #"key2", nil];
}
NSDictionary *myDictionary = [self myFunction]
NSString *string1 = [myDictionary objectForKey:#"key1"];
NSString *string2 = [myDictionary objectForKey:#"key2"];