CODEWITHSUNDEEP
c++hex
Quaker
Quaker

Reputation: 1553

Getting hex through Cin

Why doesn't this code work?

int x;
cin >> x;

With the input of 0x1a I get that x == 0 and not 26.

Why's that?

Upvotes: 21

Views: 43640

Answers (5)

Karol D
Karol D

Reputation: 391

Actually, You can force >> operator to get and properly interpret prefixes 0 and 0x. All you have to do is to remove default settings for std::cin:

std::cin.unsetf(std::ios::dec);
std::cin.unsetf(std::ios::hex);
std::cin.unsetf(std::ios::oct);

Now, when you input 0x1a you will receive 26.

Upvotes: 29

AlbertFG
AlbertFG

Reputation: 157

#include<iostream>
using namespace std;

int main()
{
    int data[16];
    cout << "enter the 16 hexadecimal numbers\n";
    for(int i = 0;i < 16;i++)
    {
        if(cin >> hex >> data[i])
            cout << "input worked\n";
        else{
            cin.clear();
            cout << "invalid input\n";
        }
    }
}

Upvotes: 0

Component 10
Component 10

Reputation: 10497

Your code should read:

int x;
cin >> hex >> x;

By default cin will expect any number read in to be decimal. Clearly, 0x1a is not a valid decimal and so the conversion cannot take place. To get it to work we have to use the stream modifier hex which prompts cin to expect number conversion from hexadecimal rather than decimal.

The 0x prefix is optional in this case so the input 10 would be read and stored as decimal 16.

Upvotes: 2

David G
David G

Reputation: 96810

Think of << and >> when using std::cout/std::cin like so:

std::cout << x means get the value from x

std::cin >> x means put the value into x

Notice the directions in which the operators are pointing. That should give you a hint as to what they do when using these functions.

The reason that you are getting 0 as a result and not 26 is because std::cin will parse the all non numeric characters from your input. After all, x is an int, it won't recognize 0x as a part of a hexadecimal number. It would of had the same behavior if the input was 9x2 (the result would simply be 9).

Upvotes: 3

sean
sean

Reputation: 530

I believe in order to use hex you need to do something like this:

cin >> hex >> x;
cout << hex << x;

you can also replace hex with dec and oct etc.

Upvotes: 39

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