CODEWITHSUNDEEP
c++numberslong-integer
MaestroMaus
MaestroMaus

Reputation: 375

Strange Number Conversion C++

So I have the following code:

#include <iostream>
#include <string>
#include <array>

using namespace std;

int main()
{
    array<long, 3> test_vars = { 121, 319225, 15241383936 };
    for (long test_var : test_vars) {
        cout << test_var << endl;
    }
}

In Visual Studio I get this output:

  1. 121
  2. 319225
  3. -1938485248

The same code executed on the website cpp.sh gave the following output:

  1. 121
  2. 319225
  3. 15241383936

I expect the output to be like the one from cpp.sh. I don't understand the output from Visual Studio. It's probably something simple; but I'd appreciate it nonetheless if someone could tell me what's wrong. It's has become a real source of annoyance to me.

Upvotes: 1

Views: 336

Answers (1)

user4290866
user4290866

Reputation:

The MSVC uses a 4Byte long. The C++ standard only guarantees long to be at least as large as int. Therefore the max number representable by a signed long is 2.147.483.647. What you input is too large to hold by the long and you will have to use a larger datatype with at least 64bit.

The other compiler used a 64bit wide long which is the reason why it worked there.

You could use int64_t which is defined in cstdint header. Which would guarantee the 64bit size of the signed int.

Your program would read:

#include <cstdint>
#include <iostream>
#include <array>

using namespace std;

int main()
{
    array<int64_t, 3> test_vars = { 121, 319225, 15241383936 };
    for (int64_t test_var : test_vars) {
        cout << test_var << endl;
    }
}

Upvotes: 7

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