Επεξεργασία

Κοινή χρήση μέσω

Compiler Warning (level 4) C4770

  • Άρθρο

partially validated enum 'symbol' used as index

The compiler warns if an enum value is cast or aliased to an integer type, but the result isn't checked for non-negative or excessive values.

Remarks

This warning is new in Visual Studio 2013. It's not enabled by default. To enable it as a level 1 warning, use /w14770. For information on how to disable warnings by compiler version, see Compiler warnings by compiler version.

Example

The following code produces warning C4770:

// c4770.cpp
// compile by using: cl /GL /w14770 c4770.cpp

enum E { a  0, b, c, E_MAX };

int main(int argc, char *argv[])
{
    const E e1 = E(argc); // value unknown at compile time

    if ((int)(e1) >= E_MAX)
        return 0;

    const int n = e1 + e1;  // C4770 partially validated enum used as index

    return argv[n][n];
}

To fix the warning, you could cast the value in the check to unsigned int, which implicitly forces a non-negative value:

    if ((unsigned int)(e1) >= E_MAX) 
        return 0;

Or, explicitly check for a non-negative value:

    if ((int)(e1) >= E_MAX || (int)(e1) < 0)
        return 0;