Compiler Warning (level 4) C4389

'equality-operator' : signed/unsigned mismatch

Remarks

An == or != operation involved signed and unsigned variables. This could result in a loss of data.

One way to fix this warning is if you cast one of the two types when you compare signed and unsigned types.

Example

The following example generates C4389:

// C4389.cpp
// compile with: cl /EHsc /W4 C4389.cpp

int main()
{
   int a = 9;
   unsigned int b = 10;
   int result = 0;

   if (a == b)   // C4389
      result = 1;
   else
      result = 2;

   if (unsigned(a) == b) // OK
      result = 3;
   else
      result = 4;

   return result;
}

See also

Compiler Warning C4018
Compiler Warning (Level 4) C4388