15.7 Efficiency

The design of the complex class addresses efficiency concerns.

The simplest functions are declared inline to eliminate function call overhead.

Several overloaded versions of functions are provided when that makes a difference. For example, the pow function has versions that take exponents of type double and int as well as complex, since the computations for the former are much simpler.

The standard C math library header math.h is included automatically when you include complex.h. The C++ overloading rules then result in efficient evaluation of expressions like this:

double x;
complex x = sqrt(x);

In this example, the standard math function sqrt(double) is called, and the result is converted to type complex, rather than converting to type complex first and then calling sqrt(complex). This result falls right out of the overload resolution rules, and is precisely the result you want.