V665. Possible incorrect use of '#pragma warning(default: X)'. The '#pragma warning(push/pop)' should be used instead.

The analyzer has detected an incorrect sequence of '#pragma warning' directives in the code.

Programmers often assume that warnings disabled with the "pragma warning(disable: X)" directive earlier will start working again after using the "pragma warning(default : X)" directive. It's not so. The 'pragma warning(default : X)' directive sets the 'X' warning to the DEFAULT state which is quite not the same thing.

Imagine that a file is compiled with the /Wall switch used. The C4061 warning must be generated in this case. If you add the "#pragma warning(default : 4061)" directive, this warning will not be displayed, as it is turned off by default.

The correct way to return the previous state of a warning is to use directives "#pragma warning(push[ ,n ])" and "#pragma warning(pop)". See the Visual C++ documentation for descriptions of these directives: Pragma Directives. Warnings.

Here's an example of incorrect code:

#pragma warning(disable: 4001)
....
//Correct code triggering the 4001 warning
....
#pragma warning(default: 4001)

The 4001 warning will be set to the default state in this sample. But the programmer must have intended to return the previous state used before it had been disabled. For this purpose, we should use the 'pragma warning(push)' directive before turning off the warning and the 'pragma warning(pop)' directive after the correct code.

This is the fixed code:

#pragma warning(push)
#pragma warning(disable: 4001)
....
// Correct code triggering the 4001 warning
....
#pragma warning(pop)

Library developers should pay special attention to the V665 warning. Careless warning customization may cause a whole lot of troubles on the library users' side.

Good article about this theme: "So, You Want to Suppress This Warning in Visual C++".

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