I read about the std::abs() function when browsing cppreference.
On that page I have also seen a std::labs() function. Which has the same prototype as one of the std::abs() overloads (the one for long).
long abs( long n );
long labs( long n );
and
long long abs( long long n );
long long llabs( long long n );
So,
std::labs() does?std::labs()?std::abs() and std::labs()?C++11 was when std::labs and std::llabs were added. This was part of the partial syncing done to the C++ standard library with the C99 standard library.
You don't really need it in C++ code, because we had a long overload of std::abs since about forever. But if you have some C code (that by sheer coincidence also compiles with a C++ compiler), and it uses labs, you can build it with a C++11 compiler and standard library.
In retrospect, there is one marginally useful use case for these functions. And that is when an attempt to use std::abs is ambiguous. For instance:
template<typename T>
T run_func(T (&f)(T)) {
return f({});
}
Then trying to call run_func(std::abs); is ill-formed. We need to either specify the template argument explicitly or cast std::abs to the proper type. On the other hand run_func(std::labs); isn't ambiguous, and not too verbose.
Still, not too useful.
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