Understanding the Role of the \'register\' Keyword in C

Demystifying 'register' Keyword in C

In C , programmers encounter two similar code snippets that can seem indistinguishable at first glance:

int x = 7;

and

register int x = 7;

What's the subtle difference between these two lines of code?

The answer lies in the 'register' keyword. In C , 'register' is an optional keyword that serves as a suggestion to the compiler. It implies that the variable 'x' should be stored in a processor register, which is significantly faster than accessing it from memory.

It's important to note that the compiler has the ultimate decision on whether or not to honor this suggestion. There are various factors that may influence its choice, such as the availability of processor registers, the size of the variable, and the optimization level of the compiler.

According to the C expert Herb Sutter, "A register specifier has the same semantics as an auto specifier..." This implies that the compiler automatically decides where to store the variable, including processor registers or memory, based on optimization criteria.

Therefore, the 'register' keyword in C is a hint that can potentially optimize code performance, but it doesn't guarantee it. The compiler remains in control and makes the final decision on variable storage.

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