What Happens When an Inline Function Cannot be Inlined?

What Happens When an Inline Function Cannot be Inlined?

Not every function that is declared inline can actually be inlined by the compiler. A function that has local variables, loops, or an extensive amount of code cannot be inlined efficiently. In this case, the compiler may suppress the inlining request, and convert the function to a static function. Consequently, numerous copies of the same function will be generated (one copy per translation unit), resulting in a longer compilation time. Additionally, the linker has to compare these copies to ensure they are all identical, and then remove all but one of the excess copies–a time consuming process. The result is equivalent to a simple external function, only with the additional compile and link time. Therefore, you should use the inline specifier judiciously–in very short functions (“getters” and “setters”), or better still, avoid using it altogether, and let the compiler inline the suitable functions automatically.


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