为什么numeric_limits :: min为int返回负值但是为float / double返回正值？

Question

Why does numeric_limits::min return a negative value for int, but positive values for eg float and double?

#include<iostream>
#include<limits>

using namespace std;

int main() {
  cout << "int: " << numeric_limits<int>::min() << " "
       << "float: " << numeric_limits<float>::min() << " "
       << "double: " << numeric_limits<double>::min() << "\n";
  return 0;
}

Output:

int: -2147483648 float: 1.17549e-38 double: 2.22507e-308

From cppreference:

Returns the minimum finite value representable by the numeric type T.

For floating-point types with denormalization, min returns the minimum positive normalized value. Note that this behavior may be unexpected , especially when compared to the behavior of min for integral types. To find the value that has no values less than it, use numeric_limits::lowest .

min is only meaningful for bounded types and for unbounded unsigned types, that is, types that represent an infinite set of negative values have no meaningful minimum.

Answer 1

By definition, for floating types, min returns the smallest positive value the type can encode, not the lowest .

If you want the lowest value, use numeric_limits::lowest instead.

Documentation: http://en.cppreference.com/w/cpp/types/numeric_limits/min

As for why it is this way, I can only speculate that the Standard committee needed to have a way to represent all forms of extreme values for all different native types. In the case of integral types, there's only two types of extreme: max positive and max negative. For floats there is another: smallest possible.

If you think the semantics are a bit muddled, I agree. The semantics of the related #define s in the C standard are muddled in much the same way.

Answer 2

It's unfortunate, but behind similar names completely different meaning lies. It was kinda carried over from C, where DBL_MIN and INT_MIN has the very same "problem".

As not much can be done, just remember what means what.