compiler-warning-level-3-c4800.md

description	title	ms.date	f1_keywords	helpviewer_keywords	ms.assetid
Learn more about: Compiler Warning (level 4) C4800	Compiler Warning (level 4) C4800	03/14/2019	C4800	C4800	4f409799-a250-45ed-bb5f-657691b0d9f7

Compiler Warning (level 4) C4800

::: moniker range=">= msvc-160" Visual Studio 2019 and later:

Implicit conversion from 'type' to bool. Possible information loss ::: moniker-end

C4800 is a level 3 warning in Visual Studio 2015 and earlier:

'type' : forcing value to bool 'true' or 'false' (performance warning)

This warning is generated when a value is implicitly converted into type bool. Typically, this message is caused by assigning int variables to bool variables where the int variable contains only values true and false, and could be redeclared as type bool. If you can't rewrite the expression to use type bool, then you can add "!=0" to the expression, which gives the expression type bool. Casting the expression to type bool doesn't disable the warning, which is by design.

::: moniker range=">= msvc-150" This warning is not emitted in Visual Studio 2017. ::: moniker-end

::: moniker range=">= msvc-160" This warning is off by default starting in Visual Studio 2019. Use /wn4800 to enable C4800 as a level n warning, or /Wall to enable all warnings that are off by default. For more information, see Compiler Warnings That Are Off By Default. ::: moniker-end

Example

The following sample generates C4800 and shows how to fix it:

// C4800.cpp
// compile with: /W4 /w44800
int main() {
   int i = 0;

   // To fix, instead try:
   // bool i = 0;

   bool j = i;   // C4800
   j++;
}