The latter is, since C++11, an alternative null pointer constant.Visual Studio 2019 version 16.1 Preview 3 ships with the first side-by-side minor versions of the v142 MSVC toolset. Null pointer constants are what makes NULL work to initialize and compare null pointers, by having NULL expand either to an integer literal with value 0 or to nullptr. Therefore overload resolution may be affected by the specific value passed as argument.

This also applies to true which has value 1. Values other than 0, even if an integer literal, are never null pointer constants and therefore cannot be converted to pointers implicitly. Note however, that you still have this problem if you use a literal 0 in your code and yes, it can affect overload resolution. With /std:c++20 or higher this is also set by default, if I am not mistaken.

If you give MSVC the flag /permissive- to make it behave more standard-conform and implement the new rule. MSVC is not implementing the defect report with default flags and still follows this old rule, according to which the expression false is a null pointer constant. Before that every integral constant expression with value 0 was a null pointer constant. However this rule is only in place since resolution of CWG issue 903.

Although it has value 0, false is not an integer literal. The correct behavior according to the standard is to treat only integer literals with value 0 as null pointer constants. MSVC treats the expression false as a null pointer constant.Ī null pointer constant can be implicitly converted to any pointer type, resulting in a null pointer value. Test(false) // won't compile anymore: error C2668: 'test' : ambiguous call to overloaded functionīTW I'm also using VS2012, which has the same behavior with the same test codes. i.e., you have a test(bool* pb) method and an overloaded version with a pointer: test(int* pv) bool test(bool* pb) In addition, this behavior can cause issues with overloaded methods. Line, which sounds to me what the normal behavior should be. I have tried online compilers tool, and they do not accept the test(false) Test(true) // won't compile: error C2664: 'test' : cannot convert parameter 1 from 'bool' to 'bool *' Test(false) // compiles (not what I was expecting) I don't understand this: whis can the false keyword be used as NULL (or nullptr)? Below the test code: bool test(bool* pb) I'm using native C++ with Visual Studio 2019 16.11.8.

Visual studio 2019 c++