Why compareBoolExpressionWithInt?

[Sander Bouwhuis]

I have the following code (m_bEnabled is a bool):

1. case WM_ENABLE: // 0x00a
2.   // Is the state changing?
3.   if((wParam == 0 ? false : true) != m_bEnabled)
4.   {
5.     // Change the state
6.     m_bEnabled = !m_bEnabled;
7.   }
8.   break;

CppCheck v1.88 gives error compareBoolExpressionWithInt on line 3.
Why is that? The wParam gets compared to an int (0), after which everything between the round brackets becomes either 'false' or 'true'. Then that gets compared to m_bEnabled, which is a bool.

Why does this warning occur?

[versat]

With the following simplified C++ code i can reproduce it with 1.89 dev:

bool f(int a, bool b)
{
    if ((a == 0 ? false : true) != b) {
        b = !b;
    }
    return b;
}

Output:

$ g++ -fsyntax-only fp_compareBoolExpressionWithInt.cpp && ./cppcheck --enable=warning --debug fp_compareBoolExpressionWithInt.cpp
Checking fp_compareBoolExpressionWithInt.cpp ...

##file fp_compareBoolExpressionWithInt.cpp
1: bool f ( int a@1 , bool b@2 )
2: {
3: if ( ( a@1 == 0 ? false : true ) != b@2 ) {
4: b@2 = ! b@2 ;
5: }
6: return b@2 ;
7: }

##Value flow
Line 3
  a possible 0
  == possible 1
  0 always 0
  ? possible {0,1}
  false always 0
  : always 1
  true always 1
fp_compareBoolExpressionWithInt.cpp:3:33: warning: Comparison of a boolean expression with an integer. [compareBoolExpressionWithInt]
    if ((a == 0 ? false : true) != b) {
                                ^

Looks like a false positive to me.
If i am not missing anything this warning should not be shown.

[versat]

I have created a ticket for this: https://trac.cppcheck.net/ticket/9304

[Sander Bouwhuis]

Thanks. It's always good news when false positives can be fixed.

I rewrote it to this:

if((wParam != 0) != m_bEnabled)

Now CppCheck doesn't fail anymore.

[Ken-Patrick Lehrmann]

This issue should be fixed with https://github.com/danmar/cppcheck/pull/2131

[Fabio]

Just encountered this issue, but on a different type of code.

#include <variant>

template <typename Variant>
auto vcheck1() {
    return std::variant_size_v<Variant>-1; // <- this one has the issue
}

template <typename Variant>
auto vcheck2() {
    return std::variant_size<Variant>::value-1; // <- this one has not
}

Problem exists in trunk.