Thread: Preprocessor help required

  1. #1
    Registered User
    Join Date
    May 2012

    Preprocessor help required

    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
    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);
    #undef U
    C File
    // 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;                    \
    #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

    Last edited by Salem; 05-06-2012 at 02:18 PM. Reason: Fixed train-wreck formatting

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    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;
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
    Registered User
    Join Date
    May 2012
    Thanks Salem

    for Hitech Complier it is "--pre" and it gave me answer of my question



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