changing a single bit of an unsigned interger variable

[3bottles]

Hi,
What i'm trying to write a code that would allow me change a single bit of a variable. So I've tried to store it in an array so that its possible for me to change a single bit of the variable by simply changing the value of the array index.
However this doesn't seem to work. See extract of code below.

Help please...ideas, suggestions?

typedef u_int32_t UInt32;
UInt32 value = 0xFFFFFFFF;
int index = 4;

UInt32* var = new UInt32[32];
*var = value;
var[index] = 0;

cout<<hex<<*chan<<endl;

[scruggsy]

Hi,
What i'm trying to write a code that would allow me change a single bit of a variable. So I've tried to store it in an array so that its possible for me to change a single bit of the variable by simply changing the value of the array index.
However this doesn't seem to work. See extract of code below.

Help please...ideas, suggestions?

typedef u_int32_t UInt32;
UInt32 value = 0xFFFFFFFF;
int index = 4;

UInt32* var = new UInt32[32];
*var = value;
var[index] = 0;

cout<<hex<<*chan<<endl;

That's not going to work.
To manipulate individual bits you can use the bit-wise operators or a bitset. You should probably learn how the bit-wise operators work since that is rather fundamental to an understanding of how computer store and manipulate data.
Examples in binary:
0001 | 0010 = 0011
0111 & 1001 = 0001
~0101 = 1010

[weaknessforcats]

You should probably learn how the bit-wise operators work

Actually, for C++ you should learn the bitset<> template. The bitwise operators are very low level and are rarely used in C++ unless the C++ is being written by a C programmer.

[3bottles]

That's not going to work.
To manipulate individual bits you can use the bit-wise operators or a bitset. You should probably learn how the bit-wise operators work since that is rather fundamental to an understanding of how computer store and manipulate data.
Examples in binary:
0001 | 0010 = 0011
0111 & 1001 = 0001
~0101 = 1010

Thanks. But my reluctance to masking is that there are 32 possible values for index. So that would mean writing 32 possible conditions. Isn't there a shorter way of doing this?

[scruggsy]

Thanks. But my reluctance to masking is that there are 32 possible values for index. So that would mean writing 32 possible conditions. Isn't there a shorter way of doing this?

Yes, use the left shift operator.
More examples in binary:
1 << 0 = 1
1 << 1 = 10
1 << 2 = 100 etc...

This means all you need to know is the position of the bit (0 thru 31) you want to change. Use the shift operator to get your mask, then & or | to flip your bit.

[weaknessforcats]

Again, I say: Use a bitset.

[code=cpp]
bitset<32> thebits;
thebits.set(19) ; //bit 19 is 1
thebits.reset(1 9); //bit 19 is 0
thebits.test(19 ); //true if bit 19 is 1
//etc
[/code]

You can use an enum to name your bits:
[code=cpp]
enum bits {POWER_ON, PAPER_LOADED, TONER_LOW};
[/code]

then use the enum names instead of the bit number.

Those bitwise operators are supposed to remain in C.