Question 238219 in Visual Studio Code Question posted in
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Visual Studio Code – Logical vs. bitwise operators. Both are wrong?

When I use the following minimal code in an C++ console application in Visual Studio 2019, I get two warnings, which are completely opposite.

int main()
{
    unsigned char op1 = 0x1;
    unsigned char op2 = 0x3;
    unsigned char result1 = op1 | op2;
    unsigned char result2 = op1 || op2;
}

The warning at unsigned char result1 = op1 | op2; is

lnt-logical-bitwise-mismatch Using bitwise ‘|’ when logical ‘||’ was probably intended.

The warning at unsigned char result2 = op1 || op2; is

lnt-logical-bitwise-mismatch Using logical ‘||’ when bitwise ‘|’ was probably intended.

This is a little bit curious.

My intention was to use the bitwise operator. How could I change the line unsigned char result1 = op1 | op2;, so that the Visual Studio 2019 warning goes away?

The warning is not from the compiler; the output is error-free.
Maybe it comes from the ReSharper C++ module or from Visual Studio code analysis.

(Of course I could ignore that warning, but in the original code there are a lot of them, because there a lot of unsigned char bitwise operations.)

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2

Answers


  1. 0

    lnt-logical-bitwise-mismatch is a Visual Studio linter rule. It tells you that logical operators should only be used with booleans:

    bool op1 = true;
bool op2 = false;
bool result2 = op1 || op2;

    and bitwise operatos should only be used with integers, not chars:

    unsigned int op1 = 0x1;
unsigned int op2 = 0x3;
unsigned int result2 = op1 | op2;

    See https://learn.microsoft.com/en-us/cpp/ide/lnt-logical-bitwise-mismatch?view=msvc-170 for more details

    If you don’t want this warning, you can configure the linter in "Options" -> "Text Editor" -> "C/C++" -> "Code Style" -> "Linter": https://learn.microsoft.com/en-us/cpp/ide/cpp-linter-overview?view=msvc-170#configure-the-linter

    I’m not saying that these rules make sense. I’m just answering why you get the squiggles and how you can avoid it. The usefulness of these rules is a different question.

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  2. 0

    You can

    • configure the linter in "Options" -> "Text Editor" -> "C/C++" -> "Code Style" -> "Linter" as suggested by the other answer.
      I do not know if that is saved to the project file to switch off the warning for other people

    • type cast to integer (or potentially to unsigned char(?)) as suggested in the comments. You may //explain why.

    • change the type of the variables. Presumably you use char for some reason (input output communication…); then the type cast may take place somewhere closer to that reason

    • possibly there is #pragma or something to tell the linter to shut up (??)
      (Or probably not — because type cast is a simple solution.)

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