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I want to change a bit an integer variable in C/CSS for pic.
Ex: change some bit to turn another number.
15 = 0b00001111 -> 0b00001101 = 13.
2 answers
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General solution in C
As a general rule, to "delete" a bit, that’s it:
valor &= ~( 1 << bitPos);
and to "light up," that’s it:
valor |= 1 << bitPos;
whereas bitPos is the bit position, zero being the rightmost.
See working on IDEONE.
If you want to manipulate more than one bit at a time, can do so too:
int valor = 15 // 0b00001111;
int mascara = 70 // 0b01000101;
//BIT: 76543210
resultado1 = valor | mascara; // 0b01001111 ("acendi" os bits 0,2 e 6)
resultado2 = valor & ~mascara; // 0b00001010 ("apaguei" os bits 0,2 e 6)
See working on IDEONE
Example:
int valor = 15 // 0b00001111;
valor &= ~( 1 << 0 ); // valor = 14 ( 0b00001110 ) - "apagamos" o bit 0
valor |= 1 << 5; // valor = 46 ( 0b00101110 ) - "acendemos" o bit 5
valor &= ~( 1 << 1 ); // valor = 44 ( 0b00101100 ) - "apagamos" o bit 1
valor |= 1 << 0; // valor = 45 ( 0b00101101 ) - "acendemos" o bit 0
Functions of the CCS
According to Mr Bruno, there are bit_set(número, bit) and bit_clear(número, bit), see corresponding answer.
Of curiosity, if it were to Arduino:
Just to complement, if someone is interested in Arduino equivalent, we have similar functions to those of CCS:
https://www.arduino.cc/en/Reference/HomePage
We have these two functions:
Whereas x is the value to be changed, and n the bit to be changed, being 0 the right most bit.
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The CCS has the functions bit_set(número, bit), which arrow the bit as 1 and bit_clear(número, bit) that resets the bit as 0!
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The prefix 0b for binary numbers is not standard for C, it is an extension of gcc (and probably other compilers, but as far as I know the Microsoft C compiler, for example, does not have this extension).
– zentrunix
@Josex I could have mentioned that it is C++14 (by the way, I think it was ridiculous that it took so long), although in the context of the question I put it for visualization (and the author used it in the original code, which was the target of the answer). Anyway, I passed for comments not to confuse, in case someone decides to copy and compile as it is in some context different from the author.
– Bacco
C++14...there is no C14...
– zentrunix
My experience is that hexadecimals are usually used to work with bits, both in C and C++. I think it’s even more practical than using the 0b prefix.
– zentrunix
@Joséx. Or more practical, or perhaps consequence of the habit of using without for lack of option at first. For things like enums, it’s really easy to see 1,2,4,8,10,20,40,80 but for a character map or bit masks, for example, base 2 gives instant visualization. Now, of course each should wear whatever is most comfortable, provided that in the team pattern.
– Bacco