Surprise!
I've a variable like this,
NSInteger index = 0;
I'm comparing it with one of subviews count (which returns NSUInteger) like this,
if((index-1) <= [[currentmonth subviews] count])
{
NSLog(#"true");
}
else
{
NSLog(#"false");
}
This always giving false.
but If I'll do like this,
if ((index-1) <= 42) {
NSLog(#"true");
} else {
NSLog(#"false");
}
This always giving true.
I feel that, this because we can't compare NSInteger with NSUInteger correct?
I caught this issue, when I have a working solution based on this logic. But its not true at all.
I've found this, NSUInteger vs NSInteger, int vs unsigned, and similar cases
This answer gives the good explanations on this!
You should also be aware of integer conversion rules when dealing with NSUInteger vs. NSInteger:
The following fragment for example returns 0 (false) although you'd expect it to print 1 (true):
NSInteger si = -1;
NSUInteger ui = 1;
printf("%d\n", si < ui);
The reason is that the [si] variable is being implicitly converted to an unsigned int!
See CERT's Secure Coding site for an in-depth discussion around these 'issues' and how to solve them.
Related
I am trying to return the lowest number in an array.
Parameter: arrayOfNumbers - An array of NSNumbers.
Return: The lowest number in the array as an NSInteger.
The code I have thus far doesn't give me any errors, but does not pass the unit tests. What am I doing wrong?
- (NSInteger) lowestNumberInArray:(NSArray *)arrayOfNumbers {
NSNumber* smallest = [arrayOfNumbers valueForKeyPath:#"#min.self"];
for (NSInteger i = 0; i < arrayOfNumbers.count; i++) {
if (arrayOfNumbers[i] < smallest) {
smallest = arrayOfNumbers[i];
}
}
NSInteger smallestValue = [smallest integerValue];
return smallestValue;
}
This is the unit test:
- (void) testThatLowestNumberIsReturned {
NSInteger lowestNumber = [self.handler lowestNumberInArray:#[#3, #8, #-4, #0]];
XCTAssertEqual(lowestNumber, -4, #"Lowest number should be -4.");
lowestNumber = [self.handler lowestNumberInArray:#[#83, #124, #422, #953, #1004, #9532, #-1000]];
XCTAssertEqual(lowestNumber, -1000, #"Lowest number should be -1000.");
}
This method
NSNumber* smallest = [arrayOfNumbers valueForKeyPath:#"#min.self"];
will already determine the smallest number in the array, so the loop inside the method is superfluous (on top of being plain wrong, as #vikingosegundo notices).
you are comparing objects with c types, resulting im pointer addresses being compared with an int.
Beside the fact your smallest is already the smallest, as you used the KVC collection operator #min.self (see Glorfindel answer), the following code shows you correct comparison
if (arrayOfNumbers[i] < smallest)
should be
if ([arrayOfNumbers[i] compare:smallest] == NSOrderingAscending)
or
if ([arrayOfNumbers[i] integerValue] < [smallest integerValue])
Is it safe to loop over Objective-C BOOLs like so:
for (BOOL flagA = NO; flagA <= YES; flagA++)
for (BOOL flagB = NO; flagB <= flagA; flagB++)
// ...
I'd like to use this to cycle through all relevant permutations of flags in a XCTestCase.
But it appears as if YES++ is still YES at least on some platforms (hence leading to an infinite loop e.g. on iPhone 6 Plus simulator) whereas I would have expected that BOOL would just be treated as int (and hence YES++ becoming 2).
Do I have to loop over ints (my best guess) instead, or can the use of BOOL be salvaged in some convenient way?
You are all missing the point here. Drux is asking why can't he increment over BOOL, while it should be a char (8 bit value), which is perfectly incrementable.
The Answer is very easy. BOOL is sometimes a char and sometimes a bool depending on the target. From objc.h file:
#if !defined(OBJC_HIDE_64) && TARGET_OS_IPHONE && __LP64__
typedef bool BOOL;
#else
typedef signed char BOOL;
If you iterate over a bool you will get value of 1 maximum.
EDIT:
Can you please add a reference to where the semantics of ++ for bool are specified? - Drux
Even though that bool has to be 8 bits minimum, it can't have any other value than 0 or 1. Why ? Because bool a = 3 (bool equal operator) converts 3 into a bool value, which is true which is 1.
So bool a = true; a++ is the same as bool a = 2; which makes a have a value of 1
The only way I see would be adding a break in your loop to escape the infinite loop.
Another possibilities is to use simple integer and stop the for loop when counter == 2
for (BOOL flagA = NO; YES; flagA++) {
for (BOOL flagB = NO; YES; flagB++) {
// Do something
if (flagB)
break;
}
if (flagA)
break;
}
I think #Sulthan means something like this (made overly explicit on purpose):
for(int indexA = 0; indexA <= 1; indexA++){
for(int indexB = 0; indexB <= indexA; indexB++){
BOOL flagA = (indexA == 1) ? YES : NO;
BOOL flagB = (indexB == 1) ? YES : NO;
// Use your flags (booleans) here...
}
}
(Of course, you can use just the ints in place of booleans in Objective-C, if you want to avoid using too many redundant variables).
ADDENDUM: I actually performed a "Jump to definition" in Xcode (OSX project), and the part looks like this:
#if __has_feature(objc_bool)
#define YES __objc_yes
#define NO __objc_no
#else
#define YES ((BOOL)1)
#define NO ((BOOL)0)
#endif
(usr/include/objc/objc.h)
Can't "Jump to Definition" on __objc_yes (gives "Symbol Not Found")
If you're set on operating over BOOLs, then instead of:
for (BOOL flagA = NO; flagA <= YES; flagA++)
for (BOOL flagB = NO; flagB <= flagA; flagB++)
// ...
You should really be doing something this (though it is not what you want):
for (BOOL flagA = NO; flagA != YES; flagA = !flagA)
for (BOOL flagB = NO; flagB != flagA; flagB = !flagB)
// This is the only safe way to 'iterate' BOOLs
The behaviour, (BOOL)++ is not well-defined* as a BOOL can only be YES or NO. What you really should be doing is casting your BOOL to an int, and iterating over that, or refactoring your loop entirely to use int types.
The problem with casting your BOOL values to ints is, as you have pointed out, BOOL is typedef'd to something with only 8 bits of information*, therefore it only makes sense to have 255 iterations. In fact in more recent times, BOOL is not cast-able at all because it is defined as a compiler intrinsic (objc_bool, which can have values __objc_yes and __objc_no). __objc_no++ has no meaning.
TL;DR My (strong) suggestion would be to refactor your code so you are iterating over integers, and inspecting BOOLs within each iteration. Whether you cast your BOOL values, or refactor your loop is up to you, but iterating over BOOL values in the way you have indicated is both unsafe and (now, because of that) unsupported.
* In past years, the implementation details of BOOL were obvious (namely a cast to an unsigned char). With the advent of compiler intrinsics, the details are hidden (though they are likely the same). The reason they are now hidden is because you're really not supposed to rely on them, and the easiest way to stop people relying on them is to hide them from the compiler altogether.
I'm a programming newbie and I'm currently writing a conversion calc program in objective c and I'm really struggling.
I have a string representing a unsigned long long value. I need a way either when attempting to add another character to check that the new character would not go above LONG_LONG_MAX before adding it. Or deleting the last character if the value is/would be above LONG_LONG_MAX
the only possible way I could think to even try this is:
- (BOOL) isNumberStringValid:(NSString *)stringValue {
unsigned long long uVal = strtoull(stringValue.UTF8String, NULL, 0);
if (uVal <= ULLONG_MAX) return TRUE;
else return FALSE;
}
I know this doesn't work because uVal would always be <= ULLONG_MAX but I can't think of any other ways to possibly check. Can anyone help me find a way to accomplish this???
You can use the fact that strtoull() sets the value of errno to ERANGE if the given
string was out of range:
- (BOOL) isNumberStringValid:(NSString *)stringValue {
errno = 0;
unsigned long long uVal = strtoull(stringValue.UTF8String, NULL, 0);
return (errno == 0);
}
Some test (ULLONG_MAX = 264-1 = 18446744073709551615):
1234 : TRUE
18446744073709551615 : TRUE
18446744073709551616 : FALSE
1844674407370955161678 : FALSE
You can use NSNumberFormatter. Unfortunately NSNumberFormatter stores the 'maximum' value as a float, so there are some problems around the boundary of LONG_LONG_MAX. To deal with that this code checks for nil or a long long value that is negative (which means that it overflowed)
-(BOOL) isNumberStringValid:(NSString *)stringValue
{
[NSNumberFormatter setDefaultFormatterBehavior:NSNumberFormatterBehavior10_4];
NSNumberFormatter *f=[[NSNumberFormatter alloc]init];
NSNumber *max=[NSNumber numberWithLongLong:LONG_LONG_MAX];
[f setMaximum:max];
BOOL valid=NO;
NSNumber *num=[f numberFromString:stringValue];
if (num != nil) // A nil value means that input was > LONG_LONG_MAX
{
long long x=[num unsignedLongLongValue]; // A negative value here means that the input was > LONG_LONG_MAX
if (x>0)
{
valid=YES;
}
}
return valid;
}
the if statement you have is checking if uVal is less than or equal to LONG_LONG_MAX
unsigned long long uVal = (unsigned)stringValue.longLongValue;
if (uVal >= LONG_LONG_MAX) {
return YES;
}
else {
return NO;
}
I ran this and it works fine.
I'm struggling with an if Comparison - I basically want to make two comparisons - both of which need to pass - Firstly a basic if a string variable is equal to 'rec' and secondly if a strings character limit is not equal to zero.
I've tried various combinations - but this is where i'm at at the mo..
ArticleObject *A = [self.articleArray objectAtIndex:indexPath.section];
NSInteger imglength = [A.arImage length];
if([A.arRec isEqual: #"rec"] ) && (imglength !=Nil){
return 195;
}
else return 50;
I get an expected identifier error on the (imglength comparison - as in this screen shot
Can anyone shed any light for me please?
There are several things you should change:
ArticleObject *A = self.articleArray[indexPath.section];
NSInteger imglength = [A.arImage length];
if (imglength && [A.arRec isEqualToString:#"rec"]) {
return 195;
} else {
return 50;
}
Don't use Nil (or nil) with primitive types.
Your parentheses are messed up:
if([A.arec isEqualToString:#"rec"] && (imglengyb !=Nil))
^--------------//here
Maybe a better way would be:
if([A.arec isEqualToString:#"rec"] && [[A.arImage length] != 0])
I have posted screenshot of my error code.
heights output
please any one can help me?
I think the static analyzer is not seeing how _numberOfColumns can become non-zero, and hence its insistence that garbage is being assigned. You need to check that you are actually providing some means for _numberOfColumns to become non-zero.
Generally when I am writing loops that want to find the largest or the smallest value, I initialize the size variable to the largest (if I want the smallest) or smallest (if I want the largest) amount, and I think this will solve most of your issues:
float shortestHeight = FLT_MAX;
for (unsigned i = 0; i < _numberOfColumns; i++)
{
// etc.
}
The analyzer is correct. Your code will access garbage memory if _numberOfColumns is 0, thus allocating 0 bytes for heights, making heights[0] garbage. The analyzer doesn't know what values _numberOfColumns can have, but you can tell it by using assert(_numberOfColumns>0).
Take this C program for example:
int main(int argc, const char * argv[])
{
int n = argc-1;
int *a = malloc(n*sizeof(int));
for (int i=0; i<n; i++) {
a[i] = i;
}
int foo = a[0];
free(a);
return foo;
}
the size of a is determined by the number of arguments. If you have no arguments n == 0. If you are sure that your program (or just that part of your program) will always assign something greater than 0 to a, you can use an assertion. Adding assert(n>0) will tell the analyzer exactly that.