uint64 value = 0x543;
double dval = *reinterpret_cast<double*>(&value);
I want dval to be of a certain value which when written in hexadecimal looks like this "0x543". Is there any danger doing this? Do you see a more efficient way of doing this?
Thanks
Use std::bit_cast. In fact, the shown example is exactly what you are trying to do.
Related
I have hunted about quite a bit but can't find a way to get at the Hexadecimal or Binary representation of the content of a Double variable in VB6. (Are Double variables held in IEEE754 format?)
The provided Hex(x) function is no good because it integerizes its input first.
So if I want to see the exact bit pattern produced by Atn(1), Hex(Atn(1)) does NOT produce it.
I'm trying to build a mathematical function containing If clauses. I want to be able to see that the values returned on either side of these boundaries are, as closely as possible, in line.
Any suggestions?
Yes, VB6 uses standard IEEE format for Double. One way to get what you want without resorting to memcpy() tricks is to use two UDTs. The first would contain one Double, the second a static array of 8 Byte. LSet the one containing the Double into the one containing the Byte array. Then you can examine each Byte from the Double one by one.
If you need to see code let us know.
[edit]
At the module level:
Private byte_result() As Byte
Private Type double_t
dbl As Double
End Type
Private Type bytes_t
byts(1 To 8) As Byte
End Type
Then:
Function DoubleToBytes (aDouble As Double) As Byte()
Dim d As double_t
Dim b As bytes_t
d.dbl = aDouble
LSet b = d
DoubleToBytes = b.byts
End Function
To use it:
Dim Indx As Long
byte_result = DoubleToBytes(12345.6789#)
For Indx = 1 To 8
Debug.Print Hex$(byte_result(Indx)),
Next
This is air code but it should give you the idea.
I need to make a number out of the string. to do that i use well known maneuver looking something like this:
Float(string_var) rescue nil
This works nicely, however I do have a tiny, little problem. If a string is "2.50", variable I get is 2.5. Is it even possible to create Float object with 'unnecessary' 0 digit at the end? can I literally translate "2.50" into 2.50 ?
In short, the answer is no, given the question, as any Float, when examined, will use Float's to_s function, eliciting an answer without trailing zeroes.
Float will always give you a numeric value that can be interpreted any way you wish, though. In your example, you will get a float value (given a string that is a parsable float). What you are asking then, is how to display that value with trailing zeroes. To do that, you will be turning the float value back into a string.
Easiest way to accomplish that is to use the format given by one of your respondents, namely
string_var = "2.50"
float_value = Float(string_var) rescue nil # 2.5
with_trailing_zeroes = "%0.2f" % float_value # '2.50'
In Matlab this takes my two 1x102 variables (in1 and in2) and makes one that's 2x102 (out).
out = [in1 in2]
When I try this in VB/ILnumerics - with two well-formed 1x102 inputs - the output is 2x1 with both values being 0.
I'm doing it in VB like this:
Dim out As ILArray(Of Double) = {in1, in2}
It feels like I might have to extract all of the values, put them in double arrays, and pass those back in to get the results I want. What do you think?
You have theses options:
in1.concat(in2,1);
ILMath.horzcat(in1,in2);
There is also ILMath.vertcat<T>(a,b) available.
General ILArray documentation: http://ilnumerics.net/Arrays.html
I've written a simple Bag class. A Bag is filled with a fixed ratio of Temperature enums. It allows you to grab one at random and automatically refills itself when empty. It looks like this:
class Bag {
var items = Temperature[]()
init () {
refill()
}
func grab()-> Temperature {
if items.isEmpty {
refill()
}
var i = Int(arc4random()) % items.count
return items.removeAtIndex(i)
}
func refill() {
items.append(.Normal)
items.append(.Hot)
items.append(.Hot)
items.append(.Cold)
items.append(.Cold)
}
}
The Temperature enum looks like this:
enum Temperature: Int {
case Normal, Hot, Cold
}
My GameScene:SKScene has a constant instance property bag:Bag. (I've tried with a variable as well.) When I need a new temperature I call bag.grab(), once in didMoveToView and when appropriate in touchesEnded.
Randomly this call crashes on the if items.isEmpty line in Bag.grab(). The error is EXC_BAD_INSTRUCTION. Checking the debugger shows items is size=1 and [0] = (AppName.Temperature) <invalid> (0x10).
Edit Looks like I don't understand the debugger info. Even valid arrays show size=1 and unrelated values for [0] =. So no help there.
I can't get it to crash isolated in a Playground. It's probably something obvious but I'm stumped.
Function arc4random returns an UInt32. If you get a value higher than Int.max, the Int(...) cast will crash.
Using
Int(arc4random_uniform(UInt32(items.count)))
should be a better solution.
(Blame the strange crash messages in the Alpha version...)
I found that the best way to solve this is by using rand() instead of arc4random()
the code, in your case, could be:
var i = Int(rand()) % items.count
This method will generate a random Int value between the given minimum and maximum
func randomInt(min: Int, max:Int) -> Int {
return min + Int(arc4random_uniform(UInt32(max - min + 1)))
}
The crash that you were experiencing is due to the fact that Swift detected a type inconsistency at runtime.
Since Int != UInt32 you will have to first type cast the input argument of arc4random_uniform before you can compute the random number.
Swift doesn't allow to cast from one integer type to another if the result of the cast doesn't fit. E.g. the following code will work okay:
let x = 32
let y = UInt8(x)
Why? Because 32 is a possible value for an int of type UInt8. But the following code will fail:
let x = 332
let y = UInt8(x)
That's because you cannot assign 332 to an unsigned 8 bit int type, it can only take values 0 to 255 and nothing else.
When you do casts in C, the int is simply truncated, which may be unexpected or undesired, as the programmer may not be aware that truncation may take place. So Swift handles things a bit different here. It will allow such kind of casts as long as no truncation takes place but if there is truncation, you get a runtime exception. If you think truncation is okay, then you must do the truncation yourself to let Swift know that this is intended behavior, otherwise Swift must assume that is accidental behavior.
This is even documented (documentation of UnsignedInteger):
Convert from Swift's widest unsigned integer type,
trapping on overflow.
And what you see is the "overflow trapping", which is poorly done as, of course, one could have made that trap actually explain what's going on.
Assuming that items never has more than 2^32 elements (a bit more than 4 billion), the following code is safe:
var i = Int(arc4random() % UInt32(items.count))
If it can have more than 2^32 elements, you get another problem anyway as then you need a different random number function that produces random numbers beyond 2^32.
This crash is only possible on 32-bit systems. Int changes between 32-bits (Int32) and 64-bits (Int64) depending on the device architecture (see the docs).
UInt32's max is 2^32 − 1. Int64's max is 2^63 − 1, so Int64 can easily handle UInt32.max. However, Int32's max is 2^31 − 1, which means UInt32 can handle numbers greater than Int32 can, and trying to create an Int32 from a number greater than 2^31-1 will create an overflow.
I confirmed this by trying to compile the line Int(UInt32.max). On the simulators and newer devices, this compiles just fine. But I connected my old iPod Touch (32-bit device) and got this compiler error:
Integer overflows when converted from UInt32 to Int
Xcode won't even compile this line for 32-bit devices, which is likely the crash that is happening at runtime. Many of the other answers in this post are good solutions, so I won't add or copy those. I just felt that this question was missing a detailed explanation of what was going on.
This will automatically create a random Int for you:
var i = random() % items.count
i is of Int type, so no conversion necessary!
You can use
Int(rand())
To prevent same random numbers when the app starts, you can call srand()
srand(UInt32(NSDate().timeIntervalSinceReferenceDate))
let randomNumber: Int = Int(rand()) % items.count
I can not write integer into the LCD using those functions :S it shows something weird in screen
I just added the function below!!! please check it for me
I added everything needed
my_delay(1000);
LCDWriteStringXY(0,0,"Welcome..");
my_delay(1000);
LCDWriteStringXY(0,0,"Welcome...");
my_delay(1000);
LCDClear();
LCDWriteStringXY(4,0,"Testing");
LCDGotoXY(2,1);
int m=952520;
LCDWriteInt(m,6);//I can not write it!!!
void LCDWriteInt(int val,unsigned int field_length)
{
char str[5]={0,0,0,0,0};
int i=4,j=0;
while(val)
{
str[i]=val%10;
val=val/10;
i--;
}
if(field_length==-1)
while(str[j]==0) j++;
else
j=5-field_length;
if(val<0) LCDData('-');
for(i=j;i<5;i++)
{
LCDData(48+str[i]);
}
}
I think the function is written for 16-bit integers for which the maximum value would be 65535 (5 digits - same as the length of str[]). You are giving it 6 digit value, which first overruns the string when it tries to write to str[5], and then produces j = -1.
My suggestion is to either use smaller integers (16-bit only), or write another function like the one you showed us to do the same thing for larger values.
Lastly, I don't know if the if(val<0) LCDData('-') would actually ever work properly since you overwrite 'val' in the first while loop.
Use itoa function. That will help you converting integer to string and displaying on lcd. Best of luck!