Solved

# Check if an int has overflowed

Posted on 2000-03-03
Medium Priority
213 Views
If an int recieves a number which is to big, the extra bits get truncated, and the resulting number can be either positive or negative.  Is there a way to check to see if this has happened?  I know I can use a double which would simply go to infinity if such a thing was to happen but I am trying to deal with ints.
0
Question by:mvoiers
• 3
• 3
• 3
• +1

LVL 5

Expert Comment

ID: 2581073
Yep,you can use double and check it if it's higher than the highest value of unsigned int.
if(doub>0xFFFFFFFF)
......

0

LVL 5

Expert Comment

ID: 2581087
You can use
UINT_MAX
INT_MAX
....const
0

Author Comment

ID: 2581142
Maybe I was not clear.  I did state that I wanted to deal with ints and not doubles and the above solution clearly deals with doubles.  I realize I could use a double and then compare it to INT_MAX but then I would be using a double and not an int.  Say for example,

int x;
cin>>x;
cout<<x;

if the user types in INT_MAX+1 the value printed will be -INT_MAX.  Is there a way to check between the cin and cout statements that the user entered a value for int greater then int_max?

There is no way to get C++ to throw an exception is an int overflows?

0

LVL 86

Expert Comment

ID: 2581168
What OS are you using? Win32 raises a EXCEPTION_INT_OVERFLOW (SEH, not C++) in this case...
0

Author Comment

ID: 2581216
I am using Solaris.  This is a little practice assignment at work, we need to maintain portability and also ANSI C standards.
0

LVL 22

Accepted Solution

nietod earned 300 total points
ID: 2581217
jkr, I don't think that is true.

mvoiers, there is no "universal" way to detected overflow.   but there are ways for any particular mathematical operation.  so if you can provide a mathematical operation, we can suggest a way to detect a problem.

In the case you provided, the math is being done by the C++ run-time library, so you can't detect the problem.  The solution is to do the amth yourself.  Allow the user to input the number as a string, then you convert the number to an integer.  As you process each digit of the string you save the values generated from the previous digits.  If after processing any digit, the new value is less than the value you got from the previous digits, then you overflowed.
0

Author Comment

ID: 2581237
Ok...I guess I got my answer.  I was really trying to get at the fact that if I have a function that takes an int  and someone passes in something huge there is no way for that function to check if it has overflowed, unlike double which just goes to INFINITY.
0

LVL 22

Expert Comment

ID: 2581284
What do you mean by "someone"  if you mean a fucntion that calls your function, well that function has to pass an int, so it can't pass anythign larger than an int.  Overflows don't occur this way, then occur when you perform calculations or when you assign a value to a "smaller" number.  You can test for errors in these circumstances.
0

LVL 86

Expert Comment

ID: 2581344
>>jkr, I don't think that is true

"EXCEPTION_INT_OVERFLOW

The result of an integer operation caused a carry out of the most significant bit of the result."

(See help on 'GetExceptionCode()')
0

LVL 22

Expert Comment

ID: 2581455
But I don't think it is being used is it?  The x86 CPU doesn't cause an exception when this happens (probably no CPUs do.) so this would have to be manually tested for every time an int is manipulated in a way that this could happen.  That is a lot of work and it is not done in the VC code I've seen.
0

LVL 86

Expert Comment

ID: 2581551
Hmm, you're right - tested it and it didn't work ;-)
0

## Featured Post

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Container Orchestration platforms empower organizations to scale their apps at an exceptional rate. This is the reason numerous innovation-driven companies are moving apps to an appropriated datacenter wide platform that empowers them to scale at a …
Looking for a way to avoid searching through large data sets for data that doesn't exist? A Bloom Filter might be what you need. This data structure is a probabilistic filter that allows you to avoid unnecessary searches when you know the data defin…
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.
###### Suggested Courses
Course of the Month4 days, 15 hours left to enroll