Steve Graegert wrote: > > I think passing as const & would be more efficient since passing by > > value would involve copying the value whereas passing by const & would > > skip this step. Am I right? Or is there something else? > > I have seen many programs making use const reference parameters in > order to inform the compiler that the parameter is read-only, and > hence should be better optimized. > > Unfortunately, this intent is at odds with the C++ language > definition. The const keyword says that the storage may not be > modified through the given name. What it does not say is that the > storage cannot be modified through some other name. > > With the exception of variables directly declared const, which means > you can only initialize them, const is basically ineffective a > improving run-time performance. It does, however, catch errors in the > programming process. Using a const qualifier still allows the compiler to optimise the caller. E.g. if it computes a complex expression involving a variable, passes a pointer/reference to that variable to a function, then subsequently uses the result of the expression, it doesn't have to re-compute the expression if the pointer/reference has a const qualifier. In any case, I suspect that the OP was talking primarily about passing references rather than values, rather than about const qualifiers per se. -- Glynn Clements <glynn@xxxxxxxxxxxxxxxxxx> - To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
