CODEWITHSUNDEEP
c++
Minja
Minja

Reputation: 786

Why does the data type long support a maximum number equal to long long's?

So I was doing some testing with the new data type long long when I stumbled upon a little "problem" (example came from C++ Primer 6th edition). I was using the climits library to tell me the maximum number supported by long and long long and both came out to 9223372036854775807. How is that possible?

#include <iostream> 
#include <climits>

int main()
{
    std::cout << "int size is " << sizeof(int) << " bytes." << std::endl;
    std::cout << "short size is " << sizeof(short) << " bytes." << std::endl;
    std::cout << "long size is " << sizeof(long) << " bytes." << std::endl;
    std::cout << "long long size is " << sizeof(long long) << " bytes." << std::endl;

    std::cout << "Maximum values: " << std::endl;
    std::cout << "int: " << INT_MAX << std::endl;
    std::cout << "short: " << SHRT_MAX << std::endl;
    std::cout << "long: " << LONG_MAX << std::endl;
    std::cout << "long long: " << LLONG_MAX << std::endl;

    return 0;
}

Upvotes: 2

Views: 274

Answers (3)

Antoine
Antoine

Reputation: 5198

The C99 standard specifies ranges of values each type must be able to represent (§5.2.4.2.1). The specified values are minimum magnitude, so nothing prevent from having bigger range. I converted this value to the least number of bits needed to represent number in these ranges on a digital computer.

  • int should be at least 16 bits (range from –32,768 to 32,767)
  • long should be at least 32 bits (range from –2,147,483,648 to 2,147,483,647)
  • long long should be at least 64 bits (range from –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807)

Upvotes: 1

juanchopanza
juanchopanza

Reputation: 227418

It is possible because the standard mandates that long has to be at least as large as int and long long has to be at least as large at long (and at least 64 bits in C++11). So there's no contradiction.

Concerning long long in C++11, see this related question.

Since you tagged the question C++, bear in mind that the numeric limits for a given type are given in the limits header, and that what is standard in C99 (i.e. what is in <climits>) is not necessarily standard in C++, i.e. it might be implementation defined. The number of bits in long long (or, more explicitly, its value range) is an example of a standard in C that only became standard in C++11.

Upvotes: 5

Rich Drummond
Rich Drummond

Reputation: 3509

Because you are running on a 64-bit machine where the compiler implements 'long' and 'long long' as a 64-bit integer.

If you were to compile this on for a 32-bit machine you'd see a difference. For example:

$ g++ -m32 size.cpp
$ ./a.out 
int size is 4 bytes.
short size is 2 bytes.
long size is 4 bytes.
long long size is 8 bytes.
Maximum values: 
int: 2147483647
short: 32767
long: 2147483647
long long: 9223372036854775807

Upvotes: 5

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