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using jb of a unsigned char in c

heyvaert vincent

hello,
I would like to do a bit test of a unsigned char variable. It's like a jb in assembler.

here is my code in c.


unsigned char displ;
unsigned char display3 = 0xA8;
unsigned char i;
sbit display_data = P1^0;

displ = display3;
for (i=0; i<7; i++) {
        if (displ^0 == 1){
        display_data = 0;
        }
        else {
        display_data = 1;
        }
        displ>>=1;
}


I don't have any warning or error, but the result of test is wrong.
is it possible to do in c?

tkx.

Parents
  • 0 in reply to Christoph Franck

    The standard, portable way to test bits in C has been presented -- the bitwise and (&).

    On an 8051, you can also test bits directly if the bit happens to be in an SFR or bit-addressable RAM.

    if (TI) ...

    It's generally not worth moving a bit to bit-addressable RAM just to access its bits. If a variable lives there, fine; if you just have some byte, use &.

    On the all-important braces question:

    - I agree that consistency is more important than any of the styles

    - Lef to my own devices, I go for seperate lines and indented braces:

        if (TI)
        {
        }
    else
        {
        }

    - My favorite style is not the Pascal/C "block statement" syntax, but rather the Algol/Modula/Ada style where the grammar allows multiple statements in control structures:

       if (TI)
   else
       for ()
       end
   end

    The begin/end {/} delimiters are grammatically unnecessary and just visual clutter. But there's nothing to be done about the C grammar at this point. Unfortunately, C is popular enough that nearly all the minor languages feel obliged to be "C-like" so that people will use them.

Reply
  • 0 in reply to Christoph Franck

    The standard, portable way to test bits in C has been presented -- the bitwise and (&).

    On an 8051, you can also test bits directly if the bit happens to be in an SFR or bit-addressable RAM.

    if (TI) ...

    It's generally not worth moving a bit to bit-addressable RAM just to access its bits. If a variable lives there, fine; if you just have some byte, use &.

    On the all-important braces question:

    - I agree that consistency is more important than any of the styles

    - Lef to my own devices, I go for seperate lines and indented braces:

        if (TI)
        {
        }
    else
        {
        }

    - My favorite style is not the Pascal/C "block statement" syntax, but rather the Algol/Modula/Ada style where the grammar allows multiple statements in control structures:

       if (TI)
   else
       for ()
       end
   end

    The begin/end {/} delimiters are grammatically unnecessary and just visual clutter. But there's nothing to be done about the C grammar at this point. Unfortunately, C is popular enough that nearly all the minor languages feel obliged to be "C-like" so that people will use them.

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