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understanding the syntax of MACROs setbit, clearbit

I want to create a fctn which can set or clear a bit based on the value of a variable.

I attempted to incorporate the provided macro fctns; it didn't work. It compiled, but didn't change port state. However, I don't understand the syntax of the macro.
Q: why doesn't my fctn work?
Q: how can the macro fctn work:
using a keyword 'bit' for a variable name, and not defining a variable 'var'?

Example code snippets below:
... in includes.h
#define setbit(var,bit) (var |= (0x01 << (bit)))
#define clrbit(var,bit) (var &= (~(0x01 << (bit))))

... in main.c
void changebit( UINT16 var, UINT8 bitn, bit bitstate) {
if (bitstate) setbit(var,bitn);
else clrbit(var,bitn);
}

... in main()
changebit(P7,4,bitstate);

Thank you.
David

Parents

0 david smith over 21 years ago in reply to Drew Davis

Reading your msg more carefully,

//--- A ---
UINT16 changebit( UINT16 var, UINT8 bitnum, bit bitstate) {
    if (bitstate) {
        var =  var |(0x01 << bitnum);
    }
    else {
        var &= ~(0x01 << bitnum);
    }
    return(var);
}

 P7 = changebit(P7,RED_LED,1); // LED OFF

is equivalent to:

//--- B ---

void changebit( UINT16 *var, UINT8 bitnum, bit bitstate) {
    if (bitstate) {
        *var |=  (0x01 << bitnum);  // set
    }
    else {
        *var &= ~(0x01 << bitnum);  // clr
    }
}


 changebit(&P7, RED_LED, 1); // LED OFF

?
Thanks again for your time.

Reply

0 david smith over 21 years ago in reply to Drew Davis

Reading your msg more carefully,

//--- A ---
UINT16 changebit( UINT16 var, UINT8 bitnum, bit bitstate) {
    if (bitstate) {
        var =  var |(0x01 << bitnum);
    }
    else {
        var &= ~(0x01 << bitnum);
    }
    return(var);
}

 P7 = changebit(P7,RED_LED,1); // LED OFF

is equivalent to:

//--- B ---

void changebit( UINT16 *var, UINT8 bitnum, bit bitstate) {
    if (bitstate) {
        *var |=  (0x01 << bitnum);  // set
    }
    else {
        *var &= ~(0x01 << bitnum);  // clr
    }
}


 changebit(&P7, RED_LED, 1); // LED OFF

?
Thanks again for your time.

Children

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