Compile-time function execution: Difference between revisions

Revision as of 10:37, 24 June 2015

Revision as of 06:05, 9 July 2015

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</source>

Using compile-time function evaluation, code used to compute the factorial would be exactlysimilar the same asto what one would write for run-time evaluation e.g. using C++11 constexpr.

<source lang="CPP">

#include <stdio.h>

constexpr int factorial(int n) {

return n ? (n * factorial(n - 1)) : 1;

}

constexpr int f10 = factorial(10);

int main() {

printf("%d\n", f10);

return 0;

}

</source>

In [[C++11]], this technique is known as [[C++11#constexpr – Generalized constant expressions|generalized constant expressions]](<code>constexpr</code>).<ref>{{cite web|url=http://www.stroustrup.com/sac10-constexpr.pdf|author=Gabriel Dos Reis and Bjarne Stroustrup | title=General Constant Expressions for System Programming Languages. SAC-2010. The 25th ACM Symposium On Applied Computing. | date=March 2010}}</ref> [[C++14]] [[C++14#Relaxed constexpr restrictions|relaxes the constraints]] on constexpr – allowing local declarations and use of conditionals and loops (the general restriction that all data required for the execution be available at compile-time remains).