CODEWITHSUNDEEP
c++integertype-conversion
Ivaylo Valchev
Ivaylo Valchev

Reputation: 10425

How does converting long long to int work?

For example I have the following: 

#include <iostream>

int main()
{
    long long a = 2346436346346346;

    int b = a;
    //int b = static_cast<int>(a) //same result

    std::cout << a << "\n" << b;

    std::cin.get();
}

Output:

2346436346346346
1223261034

By what logic does b take that value?

Upvotes: 1

Views: 109

Answers (3)

Baum mit Augen
Baum mit Augen

Reputation: 50111

The result of an overflowing assignment to a signed integer type is implementation defined:

If the destination type is signed, the value is unchanged if it can be represented in the destination type (and bit-field width); otherwise, the value is implementation-defined.

(4.7 Clause 3 in N4140)

So you would have to ask whoever provides your implementation what they say the result will be, the C++ standard does not say anything in regards to that.

Upvotes: 9

Dimitrios Bouzas
Dimitrios Bouzas

Reputation: 42929

According to the standard 4.7\p3 Integral conversions [conv.integral] (Emphasis Mine):

If the destination type is signed, the value is unchanged if it can be represented in the destination type; otherwise, the value is implementation-defined

Upvotes: 2

SingerOfTheFall
SingerOfTheFall

Reputation: 29986

By what logic does b take that value?

It is implementation-defined, in your case the value is truncated:

2346436346346346 in binary is:

0000000000001000 0101011000010010 0100100011101001 0111101101101010

1223261034 in binary is:
                                  0100100011101001 0111101101101010

Upvotes: 8

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