Why Use \'register int x=7;\' Instead of \'int x=7;\' in C ?

Understanding the Difference Between 'int x=7;' and 'register int x=7;' in C

The keywords 'int' and 'register' are both used in C to declare variables. The 'int' keyword simply specifies the type of the variable (in this case, an integer), while the 'register' keyword is a hint to the compiler, advising it to store that variable in a processor register instead of memory.

By using the 'register' keyword, the programmer is suggesting to the compiler that the variable is likely to be used frequently, and that storing it in a processor register would improve performance. However, it is important to note that the compiler may or may not follow this hint.

For example, if the variable 'x' is only used once or twice, or if it is unlikely to be accessed frequently, the compiler may choose to ignore the 'register' hint and store the variable in memory instead.

According to Herb Sutter in his paper entitled "Keywords That Aren't (or, Comments by Another Name)":

"A register specifier has the same semantics as an auto specifier..."

This statement implies that the 'register' keyword is essentially a suggestion to the compiler, and that the compiler is free to decide whether or not to store the variable in a processor register.

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