I am trying to perform logic based on the values of two integers. Here I am defining my integers, and I also have NSLog so I can see if the values are correct when I run the code:
int theHikeFlag = (int)[theNewHikeFlag objectAtIndex:(theID-1)];
NSLog(#"theHikeFlag: %#",theHikeFlag);
int fromTheDB = [self.detailItem hikeFlag];
NSLog(#"fromTheDB: %d",fromTheDB);
And here is the logic:
if (theHikeFlag==1) {
hikeString=#"You have";
}
else if (theHikeFlag==0) {
hikeString=#"You have not";
}
else {
if (fromTheDB==1) {
hikeString=#"You have";
}
else {
hikeString=#"You have not";
}
}
As an example of how this code is working. When theHikeFlag=1 and fromTheDB=0, the code bypasses the if and the else if and goes straight to the else and sets hikeString="You have not". This means that my result is irrelevant of theHikeFlag and is based on the fromTheDB integer.
Since you cannot store ints in an array, the line
(int)[theNewHikeFlag objectAtIndex:(theID-1)];
is not doing what you think it should. You need to pull the data from NSNumber, not cast to int.
int theHikeFlag = [[theNewHikeFlag objectAtIndex:(theID-1)] intValue];
The reason why the log output is correct is a bit funny: you made two mistakes in a row! First, you re-interpreted a pointer as an int, and then you let NSLog re-interpret it as an object again by adding a format specifier %# that is incompatible with int, but works fine with pointers! Since the int value contains a pointer to NSNumber, NSLog produces the "correct" output.
Related
I am confused as to why I get this warning:
I intiate matchObsFlag with:
int *matchObsFlag=0;
but when I run this line:
if (matchObsFlag == 1)
I get this warning. Any ideas?
You surely get a warning because you did not cast 1 as such (int*) 1 so you test an equality between different things : an address and an int.
So it is either if(matchObsFlag == (int*)1) or if(*matchObsFlag == 1) depending on what you wanna do.
int *matchObsFlag=0;
The type of matchObsFlag is int* while the constant literal is of type int. Comparison between the unrelated types is causing the warning.
matchObsFlag is a NULL pointer. matchObsFlag needs to point to a valid memory location if you wish to compare the value pointed by the pointer.
int number = 1;
matchObsFlag = &number;
Now, to compare the value, you need to dereference the pointer. So try -
if (*matchObsFlag == 1)
{
// ...
}
I want to calculate a string, which I'm doing by this:
NSExpression *expression = [NSExpression expressionWithFormat:calculationString];
float result = [[expression expressionValueWithObject:nil context:nil] floatValue];
NSLog(#"%f", result);
The problem is, when calculationstring is 1/2, the result is 0. I tried to change float with double and NSNumber and the %f to %f and %#, but I always just get 0. What to I have to change?
Also if it matters, I am in Europe, so I have commas instead of points for this value, but it shouldn't matter as I am logging with %f which shows it as points. Just for information
Basically, you just need to tell it that you are performing floating point operation,
1.0/2
1.0/2.0
1/2.0
Will all work
Typing in NSExpression is much like in C: literals that look like integers (no decimal point/comma) are treated as integers and thus use integer division. (Under integer division, 1/2 is zero. If you want 0.5, you need floating point division.) This happens when the expression is parsed and evaluated, so attempting to change the type of the result or the formatting of the output has no effect -- those things happen after parsing and evaluation.
If your calculationString is entirely under your control, it's easy to make sure that you use floating point literals anywhere you want floating point division. (That is, use 1.0/2 instead of 1/2.) If not, you'll need to change it such that it does -- here it's probably better to decompose the parsed NSExpression and change an operand rather than munge the string.
Followup edit on the "decompose" bit: String munging in content that you know to have higher-order structure is generally problematic. And with NSExpression, you already have a parser (who's smarter than a simple regex) decomposing the string for you — that is in fact what NSExpression is all about.
So, if you're working with a user-provided string, don't try to change the expression by changing the string. Let NSExpression parse it, then use properties of the resulting object to pick it apart into its constituent expressions. If your string is simply "1/2", then your expression has an array of two arguments and the function "divide:by:" — you can replace it with an equivalent function where one of the arguments is explicitly a floating-point value:
extension NSExpression {
var floatifiedForDivisionIfNeeded: NSExpression {
if function == "divide:by:", let args = arguments, let last = args.last,
let firstValue = args.first?.constantValue as? NSNumber {
let newFirst = NSExpression(forConstantValue: firstValue.doubleValue)
return NSExpression(forFunction: function, arguments: [newFirst, last])
} else {
return self
}
}
}
I think You need to User DDMathParser Which is best in this situation. I have used it in One of my project which is facing same problem as you have faced
DDMathEvaluator *eval = [DDMathEvaluator defaultMathEvaluator];
id value=[eval evaluateString:#"1/2" withSubstitutions:nil error:&error];
NSLog(#"Result %#",value);
Result 0.5
Rickster's solution worked, but had problems with expressions like 5*5/2, where the first argument (here 5*5) was not just a number.
I found a different solution here that works for me: https://stackoverflow.com/a/46554342/6385925
for people who still have this problem i did a somewhat quick fix:
extension String {
var mathExpression: String {
var returnValue = ""
for value in newString.components(separatedBy: " ") {
if value.isOperator {
returnValue += value
} else {
returnValue += "\(Double(value) ?? 0)"
}
}
return returnValue
}
var isOperator: Bool {
["+", "-", "/", "x", "*"].contains(self)
}
}
I have a function that returns a variable and I want to know how to return an array the issue is it isn't an NSArray it is just an average C array like this...
-(b2Fixture*) addFixturesToBody:(b2Body*)body forShapeName:(NSString*)shape
{
BodyDef *so = [shapeObjects objectForKey:shape];
assert(so);
FixtureDef *fix = so->fixtures;
int count = -1;
b2Fixture *Fixi[4];
while(fix)
{
count++;
NSLog(#"count = %d",count);
Fixi[count]= body->CreateFixture(&fix->fixture);
if (Fixi[count]!=0) {
NSLog(#"Fixi %d is not 0",count);
}
if (body->CreateFixture(&fix->fixture)!=0) {
NSLog(#"body %d is not 0",count);
}
fix = fix->next;
}
return *Fixi;
}
If you see some variable types you don't know it's because I'm using cocos2d framework to make a game but I'm returning a variable of b2Fixture... This code compiles however only saves the value of the first block of the array "fixi[0]" not the whole array like I want to pass
anyhelp :) thankyou
You can't return a local array. You'll need to do some kind of dynamic allocation or pull a trick like having the array inside a structure.
Here is a link to an in-depth article that should help you out.
In general returning C arrays by value is a bad idea, as arrays can be very large. Objective-C arrays are by-reference types - they are dynamically allocated and a reference, which is small, is what is passed around. You can dynamically allocate C arrays as well, using one of the malloc family for allocation and free for deallocation.
You can pass C structures around by value, and this is common, as in general structures tend to be small (or smallish anyway).
Now in your case you are using a small array, it has just 4 elements. If you consider passing these 4 values around by value is reasonable and a good fit for your design then you can do so simply by embedding the C array in a C structure:
typedef struct
{
b2Fixture *elements[4];
} b2FixtureArray;
...
-(b2FixtureArray) addFixturesToBody:(b2Body*)body forShapeName:(NSString*)shape
{
BodyDef *so = [shapeObjects objectForKey:shape];
assert(so);
FixtureDef *fix = so->fixtures;
int count = -1;
b2FixtureArray Fixi;
while(fix)
{
count++;
NSLog(#"count = %d", count);
Fixi.elements[count]= body->CreateFixture(&fix->fixture);
if (Fixi.elements[count] != 0)
{
NSLog(#"Fixi %d is not 0",count);
}
if (body->CreateFixture(&fix->fixture) != 0)
{
NSLog(#"body %d is not 0", count);
}
fix = fix->next;
}
return Fixi;
}
...
// sample call outline
b2FixtureArray result = [self addFixturesToBody...]
Whether this standard C "trick" for passing arrays by value is appropriate for your case you'll have to decide.
Note: If b2fixture is an Objective-C object make sure you understand the memory management implications of having a C array of objects references depending on the memory management model (MRC, ARC, GC) you are using.
If you need to design function or method that has to return a fixed or limited size array, one possibility is to pass a pointer to the result array to the function or method as a parameter. Then the caller can take care of allocating space, or just use a local or instance variable array. You might want the called function to sanity check that the array parameter isn't NULL before using the array.
Basically, my problem is a signed char to int and string conversion in cocoa.
I found this piece of code in an open source cocoa bluetooth application and am trying to apply it to my own.
Basically, I get a signed char output from the variable "RSSI", and want to convert it to an int and a string, the string for outputting to the log and the int for further calculation. However, no matter what I try, I cannot seem to get it converted, and just get an EXEC_BAD_ACCESS if I try outputting the signed char to the log as it is.
A typical value for the signed char would be " -57 '\307' " quoted directly from the process before it is held up by the NSLog. Here's the code:
- (BOOL)isInRange {
BluetoothHCIRSSIValue RSSI = 127; /* Valid Range: -127 to +20 */
if (device) {
if (![device isConnected]) {
[device openConnection];
}
if ([device isConnected]) {
RSSI = [device rawRSSI];
[device closeConnection];
NSLog(RSSI);
}
}
return (RSSI >= -60 && RSSI <= 20);
}
Thanks in advance.
NSLog() takes an NSString format string as its first argument, and an (optional) variable length list of variables for the format specifiers in the format string after that:
NSLog(#"RSSI: %c", RSSI);
What you've got now (NSLog(RSSI);) is simply wrong. It should be giving you compiler warnings like these:
warning: passing argument 1 of 'NSLog' makes pointer from integer without a cast
warning: format not a string literal and no format arguments
You should always pay attention to compiler warnings, not ignore them. Especially when your program crashes on the same line the warnings refer to, they should be a red flag to you that you've made a mistake.
As an aside, I should mention that NSLog() works very much like printf(). The two major differences are that NSLog's format string should be an Objective-C string literal (#"string"), not a standard C char string ("string"), and that the format specifier for an object is %#. %# is replaced by the string returned by calling the -description method on the object to be printed.
i have the following two pieces of code which i think should be identical
int temp = [[[myArray objectAtIndex:iIndex] objectAtIndex:jIndex] state];
if (temp > 0)
{
NSLog(#"TEST: %d",temp);
}
if ([[[myArray objectAtIndex:iIndex] objectAtIndex:jIndex] state] > 0)
{
NSLog(#"TEST: %d",temp);
}
state is just an int in the objects in the array with accessor like:
#property (assign)int state;
but when state is negative, the first version works (no output), but the second version outputs (for example) "TEST: -4" (?!)
is there any obvious reason why they might be different?
Since -objectAtIndex: returns an id, the compiler will not be able to know what -state should return. If you did not import the header that declares state first, or if the property state has ambiguous declaration (e.g. another class has declared #property(retain) id state before your class is imported), then the compiler may infer a wrong type for -state.
If it infers id, for instance, as all pointers are nonnegative, -4 will be implicitly viewed as 0xFFFFFFFC, thus the > 0 condition passes.
But for code 1, you have specified that temp is an int, so even if the return value of the call is 0xFFFFFFFC, it will be cast back to a signed value (-4), hence the condition fails.
The safest approach is to specify the type of -objectAtIndex:, i.e.
Foo* obj = [[myArray objectAtIndex:iIndex] objectAtIndex:jIndex];
if (obj.state > 0) {
...
I I understand it right, and the two if's are NOT in the same method, then the second one prints an unassigned variable. the fix should go like this:
if ((temp = [[[myArray objectAtIndex:iIndex] objectAtIndex:jIndex] state]) > 0)
{
NSLog(#"TEST: %d",temp);
}