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Asked: 2026-05-10T19:08:40+00:00

In a coding style question about infinite loops , some people mentioned they prefer

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In a coding style question about infinite loops, some people mentioned they prefer the for(;;) style because the while(true) style gives warning messages on MSVC about a conditional expression being constant.

This surprised me greatly, since the use of constant values in conditional expressions is a useful way of avoiding #ifdef hell. For instance, you can have in your header:

#ifdef CONFIG_FOO extern int foo_enabled; #else #define foo_enabled 0 #endif

And the code can simply use a conditional and trust the compiler to elide the dead code when CONFIG_FOO isn’t defined:

if (foo_enabled) {     ... }

Instead of having to test for CONFIG_FOO every time foo_enabled is used:

#ifdef CONFIG_FOO if (foo_enabled) {     ... } #endif

This design pattern is used all the time in the Linux kernel (for instance, include/linux/cpumask.h defines several macros to 1 or 0 when SMP is disabled and to a function call when SMP is enabled).

What is the reason for that MSVC warning? Additionally, is there a better way to avoid #ifdef hell without having to disable that warning? Or is it an overly broad warning which should not be enabled in general?

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1 Answer

  1. A warning doesn’t automatically mean that code is bad, just suspicious-looking.

    Personally I start from a position of enabling all the warnings I can, then turn off any that prove more annoying than useful. That one that fires anytime you cast anything to a bool is usually the first to go.

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