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Compiler Warning (level 1) C4293

  • Artikkeli

'operator' : shift count negative or too big, undefined behavior

If a shift count is negative or too large, the behavior of the resulting image is undefined.

Remarks

To resolve this issue, you can use a cast on the first operand to expand it to the size of the result type.

Example

The following sample generates C4293, and shows ways to fix it:

// C4293.cpp
// compile with: /c /W1
unsigned __int64 combine (unsigned lo, unsigned hi)
{
   return (hi << 32) | lo;   // C4293

   // In C, try the following line instead:
   // return ( (unsigned __int64)hi << 32) | lo;
   // In C++, try this line instead:
   // return (static_cast<unsigned __int64>(hi) << 32) | lo;
}