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Preprocessor help required

This is a discussion on Preprocessor help required within the C Programming forums, part of the General Programming Boards category; Hi I am from hardware background and not very good in C programming Can any one help me to understand ...

  1. #1
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    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
    Last edited by Salem; 05-06-2012 at 02:18 PM. Reason: Fixed train-wreck formatting

  2. #2
    and the hat of wrongness Salem's Avatar
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    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;
    mmuj likes this.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
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    Thanks Salem

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

    Cheers

    mmuj

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