CODEWITHSUNDEEP
c++integerrangeshort
Sleeping On a Giant's Shoulder
Sleeping On a Giant's Shoulder

Reputation: 997

What are the rules for printing an unsigned short value after entering an integer outside of the range of unsigned short?

#include <iostream>
#include <climits>
int main(void) {
    std::cout << SHRT_MIN << std::endl;
    std::cout << SHRT_MAX << std::endl;
    //-32768 ~ 32767 is the range
    short a;
    std::cin >> a;
    std::cout << "decimal: " << a << std::endl;//decimal
    return 0;
}

Look at the above code used to observe what happens when I enter an integer outside of the range of short.

When I enter any integer smaller than -32768, like -3333333, -32768 will be printed.

When I enter any integer bigger than 32767, like 3333333, 32767 will be printed.

Now I want to see what happens when I enter an integer outside of the range of unsigned shorts.

Here's the code:

#include <iostream>
#include <climits>
int main(void) {
    std::cout << USHRT_MAX << std::endl;
    unsigned short a;
    std::cin >> a;
    std::cout << "decimal: " << a << std::endl;//decimal
    return 0;
}

There seems to be no USHRT_MIN, but I think it is 0 that is the smallest.

So the range of unsigned short 0 ~ 65535 is the range.

When I enter any integer bigger than 65535, like 3333333, 65535 will be printed.

Now comes the part that confuses me a lot.

When I enter an integer smaller than 0, 

-1, decimal: 65535
-2, decimal: 65534
-3, decimal: 65533
-4, decimal: 65532
...
-65534, decimal: 2
-65535, decimal: 1
-65536, decimal: 65535
-65537, decimal: 65535
-65538, decimal: 65535
-65539, decimal: 65535
-3333333, decimal: 65535

From -1 to -65535, print value for a seems to have a pattern.

From -65536 to any smaller negative integer, print value for a remains 65535 all the time.

Entering an integer outside of the range of short seems like a very easy rule to follow.

Entering an integer outside of the range of unsigned short is difficult for a beginner like me to understand now.

What are the rules for printing an unsigned short value after entering an integer outside of the range of unsigned short ?

Upvotes: 1

Views: 655

Answers (1)

bruno
bruno

Reputation: 32596

Just adding a check to know if >> signal a problem :

#include <iostream>
#include <climits>

int main(void) {
    std::cout << USHRT_MAX << std::endl;
    unsigned short a;
    if (!(std::cin >> a))
      std::cout << "wrong ";
    std::cout << "decimal: " << a << std::endl;//decimal
    return 0;
}

Compilation and executions:

pi@raspberrypi:/tmp $ g++ -Wall c.cc
pi@raspberrypi:/tmp $ ./a.out
65535
-1
decimal: 65535
pi@raspberrypi:/tmp $ ./a.out
65535
-2
decimal: 65534
pi@raspberrypi:/tmp $ ./a.out
65535
70000
wrong decimal: 65535
pi@raspberrypi:/tmp $ ./a.out
65535
-70000
wrong decimal: 65535
pi@raspberrypi:/tmp $

In fact an error is signaled if you are out of range but without considering signed/not signed

Upvotes: 1

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