条件运算符。 错误CS0266无法将类型'int'隐式转换为'byte'

Question

I need some help on this conversion. I have decompiled an old dll file, because I need some small changes and I do not have the original sourcecode, but before I start making these changes I would like the original code to compile.

I only got one issue:

Error CS0266 Cannot implicitly convert type 'int' to 'byte'. An explicit conversion exists (are you missing a cast?)

I have tried many different solutions but all of the fails, so please help. How to fix this conversion?

public static byte SqlGetByte(DbDataReader sr, int col, ConnectionString connection)
{
    return (sr[col] == DBNull.Value) ? 0 : (connection.OraDb ? Convert.ToByte(sr.GetDecimal(col)) : sr.GetByte(col));
}

Answer 1

Just cast to byte

return (byte)((sr[col] == DBNull.Value) ? 0 : (connection.OraDb ? Convert.ToByte(sr.GetDecimal(col)) : sr.GetByte(col)));

// or

return (sr[col] == DBNull.Value) ? (byte)0 : (connection.OraDb ? Convert.ToByte(sr.GetDecimal(col)) : sr.GetByte(col));

---

From the specs

12.15 Conditional operator

... A conditional expression of the form b ? x : y first evaluates the condition b ...

The second and third operands, x and y, of the ?: operator control the type of the conditional expression.

• If x has type X and y has type Y then,

  • If X and Y are the same type, then this is the type of the conditional expression.
  • Otherwise, if an implicit conversion (§11.2) exists from X to Y, but not from Y to X, then Y is the type of the conditional expression.
  • Otherwise, if an implicit enumeration conversion (§11.2.4) exists from X to Y, then Y is the type of the conditional expression.
  • Otherwise, if an implicit enumeration conversion (§11.2.4) exists from Y to X, then X is the type of the conditional expression.
  • Otherwise, if an implicit conversion (§11.2) exists from Y to X, but not from X to Y , then X is the type of the conditional expression .
  • Otherwise, no expression type can be determined, and a compile-time error occurs.
• If only one of x and y has a type, and both x and y are implicitly convertible to that type, then that is the type of the conditional expression.
• Otherwise, no expression type can be determined, and a compile-time error occurs.

Given

return condition ? x(int) : y(condition ? x2(byte)) : y2(byte));

Example

byte y = 123;
int x = 234;

x = y; // y can implicitly convert to x
y = x; // error, x cant implicitly convert to y

In summary, the resulting type of the Conditional Operator wants to be an int and you are returning a byte from your method. Computer says no... At the very least you will need to cast somewhere

Answer 2

If sr[col] == DBNull.Value equates to true, you are returning 0 whereas the method returns a byte .

Change it to:

return (sr[col] == DBNull.Value) ? Convert.ToByte(0) : (connection.OraDb ? Convert.ToByte(sr.GetDecimal(col)) : sr.GetByte(col));