C error: lvalue required as unary '&' operand

问题

I have a code error but not sure what's wrong with my casting and reference.

BOOL xMBPortSerialPutByte( CHAR ucByte )
{
    CDC_Send_DATA(&((unsigned char)ucByte), 1);   // code error here
    xMBPortEventPost(EV_FRAME_SENT);
    return TRUE;
}

The CDC_Send_DATA is defined as the following:

uint32_t CDC_Send_DATA (uint8_t *ptrBuffer, uint8_t Send_length);

Here is the error message:

  port/portserial.c:139:19: error: lvalue required as unary '&' operand

Hope someone could help. Thanks!

回答1:

The cast operation causes a conversion, yielding an rvalue. An rvalue doesn't have an address, so you can't operate on it with a unary &. You need to take the address and then cast that:

CDC_Send_DATA((unsigned char *)&ucByte, 1);

But to be most correct, you should probably match the argument type in the cast:

CDC_Send_DATA((uint8_t *)&ucByte, 1);

Checking the return value would probably be a good idea too.

来源：https://stackoverflow.com/questions/18727887/c-error-lvalue-required-as-unary-operand