Logical vs. bitwise operators. Both are wrong?

Question

When I use the following minimal code in an c++ ConsoleApp in VS2019, 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 VS2019 warning goes away?

The warning is not from the compiler, the output is error-free.
Maybe it comes from Resharper c++ module or from VS 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).

It could be because of the type. It could be because the static analyzer thinks none of the expressions make sense. Or it could be a false positive. When and where are you getting these warnings? From the VS IntelliSense? From the compiler? From some third-party analyzer tool? Have you tried to search for the error in the documentation? What does it say? — 11 hours ago
Have you read learn.microsoft.com/en-us/cpp/ide/… According to the link op1 || op2 should only be used with booleans and op1 | op2 should only be used with integers, not chars — 11 hours ago
@Rodney Yes, of course, you can do this. But Microsoft doesn't recommend it and its linter gives you a warning. — 11 hours ago
@woelfchen42 it isn't a false-positive. It is a true positive of a style rule you disagree with. — 11 hours ago
Please don't post code in comments. It's not readable. Edit your question and add it there. — 10 hours ago

score 18 · Accepted Answer · 2023-08-25 10:51:22Z

18

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.

edited 10 hours ago

answered 11 hours ago

jabaa

5,6633 gold badges8 silver badges30 bronze badges

10

1

really ? What about? int *p; float *y; /* ... */; if(p && y) { do_something_();}

– 0___________

11 hours ago
1

@0___________ From the posted link: "Only use logical operators on Boolean values." Disable the linter warning, if you don't want it. It's only a linter rule and a recommendation.

– jabaa

11 hours ago
3

Do I really get downvotes for Microsoft's recommendations or is something wrong with my answer?

– jabaa

11 hours ago
1

@HolyBlackCat The sentence starts with "It tells you that…" after "lnt-logical-bitwise-mismatch is a Visual Studio linter rule." It's not my opinion. It's a fact. I'm not here to discuss whether these rules make sense or not. I want to describe when the squiggles appear and how to disable them.

– jabaa

11 hours ago
5

"Do I really get downvotes for Microsoft's recommendations" My money on the positive answer. Have an upvote to compensate.

– YSC

8 hours ago

Logical vs. bitwise operators. Both are wrong?