Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of Boost. Click here to view this page for the latest version.

Changing the Policy Defaults

The default policies used by the library are changed by the usual configuration macro method.

For example, passing -DBOOST_MATH_DOMAIN_ERROR_POLICY=errno_on_error to your compiler will cause domain errors to set ::errno and return a NaN rather than the usual default behaviour of throwing a std::domain_error exception.

[Tip] Tip

For Microsoft Visual Studio,you can add to the Project Property Page, C/C++, Preprocessor, Preprocessor definitions like:


This may be helpful to avoid complications with pre-compiled headers that may mean that the equivalent definitions in source code:


may be ignored.

The compiler command line shows:


There is however a very important caveat to this:

[Important] Important

Default policies changed by setting configuration macros must be changed uniformly in every translation unit in the program.

Failure to follow this rule may result in violations of the "One Definition Rule (ODR)" and result in unpredictable program behaviour.

That means there are only two safe ways to use these macros:

What you should not do is:

And, yes, you will find examples in our test programs where we break this rule: but only because we know there will always be a single translation unit only: don't say that you weren't warned!