/Zc:static_assert (Strict static_assert handling)

The /Zc:static_assert compiler option tells the compiler to evaluate static_assert calls with non-dependent test expressions when class or function templates are parsed.

Syntax

/Zc:static_assert
/Zc:static_assert-

Remarks

Starting with Visual Studio 17.10, /Zc:static_assert and /Zc:static_assert- have no effect. Both options are ignored to avoid breaking builds that use them. static_assert is now never evaluated when parsing class or function templates.

The /Zc:static_assert compiler option tells the compiler to evaluate a static_assert in the body of a function template or in the body of a class template member function when first parsed, if the test expression isn't dependent. If the non-dependent test expression is false, the compiler emits an error immediately. When the test expression is dependent, the static_assert isn't evaluated until the template is instantiated.

The /Zc:static_assert option is available starting in Visual Studio 2022 version 17.1. In earlier versions of Visual Studio, or if /Zc:static_assert- is specified, Visual Studio doesn't do dependent analysis if the static_assert is within the body of a function template or within the body of a member function of a class template. Instead, it only evaluates the static_assert when a template is instantiated.

The /permissive- option enables /Zc:static_assert, so it's on by default in projects that use /std:c++20 or /std:c++latest. The /Zc:static_assert- option must come after a /std:c++20, /std:c++latest, or /permissive- option on the command line.

If the compiler is in the default C++14 mode and /permissive- or /Zc:static_assert is specified, it uses /Zc:static_assert behavior. However, if it evaluates a static_assert in a template body, it also reports off-by-default warning C5254, "language feature 'terse static assert' requires compiler flag '/std:c++17'", since this behavior isn't required until C++17.

To set this compiler option in Visual Studio

1. Open the project's Property Pages dialog box. For details, see Set C++ compiler and build properties in Visual Studio.

2. Select the Configuration Properties > C/C++ > Command Line property page.

3. Add /Zc:static_assert or /Zc:static_assert- to the Additional options: pane.

See also

/Zc (Conformance)