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Learn more about: Compiler Warning (level 4) C4463 |
Compiler Warning (level 4) C4463 |
11/04/2016 |
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a07ae70c-db4e-472b-8b58-9137d9997323 |
overflow; assigning value to bit-field that can only hold values from low_value to high_value
The assigned value is outside the range of values that the bit-field can hold. Signed bit-field types use the high-order bit for the sign, so if n is the bit-field size, the range for signed bit-fields is -2n-1 to 2n-1-1, while unsigned bit-fields have a range from 0 to 2n-1.
This example generates C4463 because it attempts to assign a value of 3 to a bit-field of type int
with a size of 2, which has a range from -2 to 1.
To fix this issue, you can change the assigned value to something in the allowed range. If the bit-field is intended to hold unsigned values in the range from 0 to 3, you can change the declaration type to unsigned
. If the field is intended to hold values in the range -4 to 3, then you can change the bit-field size to 3.
// C4463_overflow.cpp
// compile with: cl /W4 /EHsc C4463_overflow.cpp
struct S {
int x : 2; // int type treats high-order bit as sign
};
int main() {
S s;
s.x = 3; // warning C4463: overflow; assigning 3
// to bit-field that can only hold values from -2 to 1
// To fix, change assigned value to fit in range,
// increase size of bitfield, and/or change base type
// to unsigned.
}