inline functions
A hint to the compiler: “paste this function’s body directly at each call site instead of doing a real call.”
inline int square(int x) { return x * x; }Why
Skips the overhead of a real call — worth it for tiny, hot-path functions. Modern compilers usually inline small functions on their own anyway with optimizations on; inline matters less for speed today and more for its other job.
The other job: getting around the One Definition Rule
A function defined in a header (and pasted into multiple .cpp files) would normally violate “defined exactly once” — inline tells the linker “these definitions are all identical, just pick one.” This is why small member functions written directly inside a class body are implicitly inline.