0 is an
int not a pointer. Almost the same goes for
though implementations of the language can differ in the details. If you
want to overload on pointer types and/or use pointer types with templates,
nullptr to signal the null pointer. The correct overload/template
parameter will then be deduced. Using
nullptr also makes the code more
readable, especially if
auto is used consistently throughout.
Reference: Item 8 in [Effective Modern C++]
auto to explicit type declarations¶
auto reduces and/or avoids:
Verbosity in variable declarations:
std::shared_ptr<Matrix> F = std::make_shared<Matrix>("Fock matrix", nso, nso); // So much typing... auto F = std::make_shared<Matrix>("Fock matrix", nso, nso); // Much better!
Problems with uninitialized variables. auto works like template type deduction, hence the right-hand side of the declaration needs to have an initializer:
int x1; // fine, but uninitialized :( auto x2; // WON'T COMPILE!!! auto x3 = 1; // fine and initialized
Problems with unintended type casts and type mismatches that are hard to impossible to catch:
std::vector<int> v; // !!! The size of a vector is of type std::vector<int>::size_type and is compiler- AND architecture-DEPENDENT unsigned sz = v.size(); // might not be correct on some compiler/machines auto size = v.size(); // size is ALWAYS of the correct type
Reference: Items 2 and 5 in [Effective Modern C++]
Mark virtual functions in derived classes with override¶
override keyword introduced in C++11 is used to mark a function in a
derived class and guarantee that it is overloading a function with the same
signature in the base class. This behavior is checked at compile time.
Prefer GiB for memory printing¶
As memory sizes get larger, we should work in giga (requires decimal printing to not round to zero) rather than mega units. As it’s what we’re computing anyways, we should work in 1024-based (mebi, gibi, etc. https://en.wikipedia.org/wiki/Gibibyte) rather than 1000-based units. As it’s a unit, put it in brackets. Note that users can supply MiB, GB, bytes, or whatever; this guideline is for output printing.
outfile->Printf(" DFHelper Memory: AOs need %.3f [GiB]; user supplied %.3f [GiB]. ", (required * 8 / (1024 * 1024 * 1024.0)),