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/Zc:noexceptTypes (C++17 noexcept rules)

  • Grein

The C++17 standard makes throw() an alias for noexcept, removes throw(type-list) and throw(...), and allows certain types to include noexcept. This change can cause a number of source compatibility issues in code that conforms to C++14 or earlier. The /Zc:noexceptTypes option specifies conformance to the C++17 standard. /Zc:noexceptTypes- allows the C++14 and earlier behavior when code is compiled in C++17 mode.

Syntax

/Zc:noexceptTypes[-]

Remarks

When the /Zc:noexceptTypes option is specified, the compiler conforms to the C++17 standard and treats throw() as an alias for noexcept, removes throw(type-list) and throw(...), and allows certain types to include noexcept. The /Zc:noexceptTypes option is only available when /std:c++17 or later is enabled. /Zc:noexceptTypes is enabled by default to conform to the ISO C++17 and later standards. The /permissive- option doesn't affect /Zc:noexceptTypes. Turn off this option by specifying /Zc:noexceptTypes- to revert to the C++14 behavior of noexcept when /std:c++17 or later is specified.

Beginning in Visual Studio 2017 version 15.5, the C++ compiler diagnoses more mismatched exception specifications in declarations in C++17 mode, or when you specify the /permissive- option.

This sample shows how declarations with an exception specifier behave when the /Zc:noexceptTypes option is set or disabled. To show the behavior when set, compile by using cl /EHsc /W4 noexceptTypes.cpp. To show the behavior when disabled, compile by using cl /EHsc /W4 /Zc:noexceptTypes- noexceptTypes.cpp.

// noexceptTypes.cpp
// Compile by using: cl /EHsc /W4 noexceptTypes.cpp
// Compile by using: cl /EHsc /W4 /Zc:noexceptTypes- noexceptTypes.cpp

void f() throw();    // equivalent to void f() noexcept;
void f() { }         // warning C5043
void g() throw(...); // warning C5040

struct A
{
    virtual void f() throw();
};

struct B : A
{
    virtual void f() { } // error C2694
};

When compiled by using the default setting /Zc:noexceptTypes, the sample generates the listed warnings. To update your code, use the following instead:

void f() noexcept;
void f() noexcept { }
void g() noexcept(false);

struct A
{
    virtual void f() noexcept;
};

struct B : A
{
    virtual void f() noexcept { }
};

For more information about conformance issues in Visual C++, see Nonstandard Behavior.

To set this compiler option in the Visual Studio development environment

  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. Modify the Additional Options property to include /Zc:noexceptTypes or /Zc:noexceptTypes- and then choose OK.

See also

/Zc (Conformance)
noexcept
Exception specifications (throw)