Compiler Warning (level 3) C4267

'var' : conversion from 'size_t' to 'type', possible loss of data

Remarks

The compiler detected a conversion from size_t to a smaller type that might truncate the value.

To fix this warning, use size_t instead of type. Alternatively, use an integral type that can represent the full range of size_t on the target platform. If the value is known at compile time and fits in the destination type, the compiler doesn't generate this warning.

Example

The following example generates C4267.

// C4267.cpp
// compile by using: cl /W4 C4267.cpp
void Func1(short) {}
void Func2(int) {}
void Func3(long) {}
void Func4(size_t) {}

int main() {
   size_t bufferSize = 10;
   Func1(bufferSize);   // C4267 for all platforms
   Func2(bufferSize);   // C4267 only for 64-bit platforms
   Func3(bufferSize);   // C4267 only for 64-bit platforms
   Func4(bufferSize);   // OK for all platforms

   // Because the compiler knows the value of bufferSize_const at compile time (because it's const),
   // it knows that converting it to short can't truncate the value so no warning is emitted
   const size_t bufferSize_const = 10;
   Func1(bufferSize_const); // No C4267

   // Because the compiler knows the value of bufferSize_big_const is 0x10000 at compile time
   // (because its const), it knows it doesn't fit in short, but does fit in int.
   const size_t bufferSize_big_const = 0x10000;
   Func1(bufferSize_big_const); // C4267
   Func2(bufferSize_big_const); // No C4267

   return 0;
}