Thread: Preprocessor help required

Hi
I am from hardware background and not very good in C programming

Can any one help me to understand this preprocessor related code PIC C programming

Code:

Header file part
//  No      Rx I/P      Tx O/P      Baud rate 103=9600
//          ena pin     ena pin     divisor   25=38400
#define UART_DEFS                           \
U(1,        C7,         C6,         103)    \
U(2,        G2,         G1,         25)
void UartPowerOnInit();
void UartEnableWakeup();
bit UartCanSleep();
void UartsSetWakeTrigger();
#define U(N,R,T,B)                                                            \
void Uart##N##TxChar(uint8_t Char);                                         \
void Uart##N##SetRxCharEvent(enum EVENT_RECIPIENT Recipient,uint8_t Event);
UART_DEFS
#undef U

C File

Code:

// Data definitions
#define U(N,R,T,B)                                           \
                                                             \
static TX_PTR      Tx##N##In;                                \
static TX_PTR      Tx##N##Out;                               \
static uint8_t     Tx##N##Buff[TX_BUFF_SIZE];                \
                                                             \
static enum EVENT_RECIPIENT Rx##N##Recipient;                \
static uint8_t              Rx##N##Event;                    \
UART_DEFS
#undef U

I am trying to understand use of token, why ## is used before and after identifier

how and why U is defined twice in same macro


Over explanation of macro use in this piece of code


Thanks in advance

mmuj

Most compilers have a flag to output just the pre-processor step (for gcc, it's the -E flag).

This shows you what the compiler sees, after all the #includes and #defines have been expanded.

My guess is you'll see things like
static TX_PTR Tx1In;
static TX_PTR Tx1Out;

static TX_PTR Tx2In;
static TX_PTR Tx2Out;