CODEWITHSUNDEEP
c++visual-studio-2012long-integerstrtolstrtoull
Honu
Honu

Reputation: 1

Why do I get wrong conversion from hex to decimal with strtoul function in Visual Studio compiler?

I am converting a string from hex to decimal. The problem is that in Visual Studio compiler the conversion returns a wrong value. However when I compile the same code in a Mac at the terminal using the g++ compiler, the value is returned correctly.

Why this is happening?

#include <string>
#include <iostream>
using namespace std;

int main()
{
    string hex = "412ce69800";

    unsigned long n = strtoul( hex.c_str(), nullptr, 16 ); 

    cout<<"The value to convert is: "<<hex<<" hex\n\n";
    cout<<"The converted value is: "<<n<<" dec\n\n";
    cout<<"The converted value should be: "<<"279926183936 dec\n\n";

    return 0;
}

output:

output file

Upvotes: 0

Views: 408

Answers (1)

phuclv
phuclv

Reputation: 41874

Because in Windows long is a 32-bit type, unlike most Unix/Linux implementations which use LP64 memory model in which long is 64 bits. The number 412ce69800 has 39 bits and inherently it can't be stored in a 32-bit type. Read compiler warnings and you'll know the issue immediately

C standard only requires long to have at least 32 bits. C99 added a new long long type with at least 64 bits, and that's guaranteed in all platforms. So if your value is in 64-bit type's range, use unsigned long long or uint64_t/uint_least64_t and strtoull instead to get the correct value.

Upvotes: 2

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