为什么函数的参数是寄存器类型

Question

sorry if my accent hurts

In C Programming, you can declare a function like this: dennis ritche 2nd ed page 84

 f(register unsigned m,register long n)

Most of the books say that the default storage type of function arguments are preferably register .

Why so? What is the need?

answer followed compiler keeps them with cpu registers but

I've not seen any difference in execution speed when using register type

Can any one explain in detail why and where and when exactly the register is used in C Programming?

thanks

Answer 1

I'd be interested in seeing which books say this.

To be honest, at this point the state of compiler technology, there is almost never any use to declaring something with a register modifier. In fact, many compilers will simply throw this out, and do whatever they want. The point is that this varies so much across architectures, compilers, and is also affected by what kinds of other optimization are done by the compiler. So, the choice of whether or not to store something in a register is a choice better left to the compiler and the use of the register modifier is usually considered an archaic antipattern.

EDIT: I incorrectly remembered register was a qualifier (which doesn't line up with the use of a type qualifier anyway, so I should have known), fixed...