How to read bits from a char variable
I needed to read the value of single bits out of a char variable. This is how I've done it.
- Create first of all a structure of bits:
struct BITS { bool b1:1; bool b2:1; bool b3:1; bool b4:1; bool b5:1; bool b6:1; bool b7:1; bool b8:1; };
- Now declare the variables in the function you're using:
void myfunction() { char cTarget; BITS b;
- Now assign a value to char and fill the BITS structure:
cout << "The full byte has a meaning of...: " << cByteRead << endl; cout << "...which is in int:" << (int)cByteRead << endl; b = *(BITS*)(&cByteRead);
- And finally display the values of the bits:
cout << b.b1 << endl; cout << b.b2 << endl; cout << b.b3 << endl; cout << b.b4 << endl; cout << b.b5 << endl; cout << b.b6 << endl; cout << b.b7 << endl; cout << b.b8 << endl;
And now, everything together:
struct BITS
{
bool b1 :1;
bool b2 :1;
bool b3 :1;
bool b4 :1;
bool b5 :1;
bool b6 :1;
bool b7 :1;
bool b8 :1;
};
void myfunction()
{
char cByteRead;
BITS b;
cByteRead = 'a';
cout << "The full byte has a meaning of...: " << cByteRead << endl;
cout << "...which is in int:" << (int)cByteRead << endl;
b = *(BITS*)(&cByteRead);
cout << b.b1 << endl;
cout << b.b2 << endl;
cout << b.b3 << endl;
cout << b.b4 << endl;
cout << b.b5 << endl;
cout << b.b6 << endl;
cout << b.b7 << endl;
cout << b.b8 << endl;
}
The mapping of the integer value of a char variable is:
Bit8 Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Int 0 0 0 0 0 0 0 0 | 0 0 0 0 0 0 0 0 1 | 1 0 0 0 0 0 0 1 0 | 2 0 0 0 0 0 0 1 1 | 3 0 0 0 0 0 1 0 0 | 4 0 0 0 0 0 1 0 1 | 5 0 0 0 0 0 1 1 0 | 6 0 0 0 0 0 1 1 1 | 7 0 0 0 0 1 0 0 0 | 8 0 0 0 0 1 0 0 1 | 9 0 0 0 0 1 0 1 0 | 10 0 0 0 0 1 0 1 1 | 11 0 0 0 0 1 1 0 0 | 12 0 0 0 0 1 1 0 1 | 13 0 0 0 0 1 1 1 0 | 14 0 0 0 0 1 1 1 1 | 15 0 0 0 1 0 0 0 0 | 16 0 0 0 1 0 0 0 1 | 17 0 0 0 1 0 0 1 0 | 18 0 0 0 1 0 0 1 1 | 19 0 0 0 1 0 1 0 0 | 20 0 0 0 1 0 1 0 1 | 21 0 0 0 1 0 1 1 0 | 22 0 0 0 1 0 1 1 1 | 23 0 0 0 1 1 0 0 0 | 24 0 0 0 1 1 0 0 1 | 25 0 0 0 1 1 0 1 0 | 26 0 0 0 1 1 0 1 1 | 27 0 0 0 1 1 1 0 0 | 28 0 0 0 1 1 1 0 1 | 29 0 0 0 1 1 1 1 0 | 30 0 0 0 1 1 1 1 1 | 31 0 0 1 0 0 0 0 0 | 32 0 0 1 0 0 0 0 1 | 33 0 0 1 0 0 0 1 0 | 34 0 0 1 0 0 0 1 1 | 35 0 0 1 0 0 1 0 0 | 36 0 0 1 0 0 1 0 1 | 37 0 0 1 0 0 1 1 0 | 38 0 0 1 0 0 1 1 1 | 39 0 0 1 0 1 0 0 0 | 40 0 0 1 0 1 0 0 1 | 41 0 0 1 0 1 0 1 0 | 42 0 0 1 0 1 0 1 1 | 43 0 0 1 0 1 1 0 0 | 44 0 0 1 0 1 1 0 1 | 45 0 0 1 0 1 1 1 0 | 46 0 0 1 0 1 1 1 1 | 47 0 0 1 1 0 0 0 0 | 48 0 0 1 1 0 0 0 1 | 49 0 0 1 1 0 0 1 0 | 50 0 0 1 1 0 0 1 1 | 51 0 0 1 1 0 1 0 0 | 52 0 0 1 1 0 1 0 1 | 53 0 0 1 1 0 1 1 0 | 54 0 0 1 1 0 1 1 1 | 55 0 0 1 1 1 0 0 0 | 56 0 0 1 1 1 0 0 1 | 57 0 0 1 1 1 0 1 0 | 58 0 0 1 1 1 0 1 1 | 59 0 0 1 1 1 1 0 0 | 60 0 0 1 1 1 1 0 1 | 61 0 0 1 1 1 1 1 0 | 62 0 0 1 1 1 1 1 1 | 63 0 1 0 0 0 0 0 0 | 64 0 1 0 0 0 0 0 1 | 65 0 1 0 0 0 0 1 0 | 66 0 1 0 0 0 0 1 1 | 67 0 1 0 0 0 1 0 0 | 68 0 1 0 0 0 1 0 1 | 69 0 1 0 0 0 1 1 0 | 70 0 1 0 0 0 1 1 1 | 71 0 1 0 0 1 0 0 0 | 72 0 1 0 0 1 0 0 1 | 73 0 1 0 0 1 0 1 0 | 74 0 1 0 0 1 0 1 1 | 75 0 1 0 0 1 1 0 0 | 76 0 1 0 0 1 1 0 1 | 77 0 1 0 0 1 1 1 0 | 78 0 1 0 0 1 1 1 1 | 79 0 1 0 1 0 0 0 0 | 80 0 1 0 1 0 0 0 1 | 81 0 1 0 1 0 0 1 0 | 82 0 1 0 1 0 0 1 1 | 83 0 1 0 1 0 1 0 0 | 84 0 1 0 1 0 1 0 1 | 85 0 1 0 1 0 1 1 0 | 86 0 1 0 1 0 1 1 1 | 87 0 1 0 1 1 0 0 0 | 88 0 1 0 1 1 0 0 1 | 89 0 1 0 1 1 0 1 0 | 90 0 1 0 1 1 0 1 1 | 91 0 1 0 1 1 1 0 0 | 92 0 1 0 1 1 1 0 1 | 93 0 1 0 1 1 1 1 0 | 94 0 1 0 1 1 1 1 1 | 95 0 1 1 0 0 0 0 0 | 96 0 1 1 0 0 0 0 1 | 97 0 1 1 0 0 0 1 0 | 98 0 1 1 0 0 0 1 1 | 99 0 1 1 0 0 1 0 0 | 100 0 1 1 0 0 1 0 1 | 101 0 1 1 0 0 1 1 0 | 102 0 1 1 0 0 1 1 1 | 103 0 1 1 0 1 0 0 0 | 104 0 1 1 0 1 0 0 1 | 105 0 1 1 0 1 0 1 0 | 106 0 1 1 0 1 0 1 1 | 107 0 1 1 0 1 1 0 0 | 108 0 1 1 0 1 1 0 1 | 109 0 1 1 0 1 1 1 0 | 110 0 1 1 0 1 1 1 1 | 111 0 1 1 1 0 0 0 0 | 112 0 1 1 1 0 0 0 1 | 113 0 1 1 1 0 0 1 0 | 114 0 1 1 1 0 0 1 1 | 115 0 1 1 1 0 1 0 0 | 116 0 1 1 1 0 1 0 1 | 117 0 1 1 1 0 1 1 0 | 118 0 1 1 1 0 1 1 1 | 119 0 1 1 1 1 0 0 0 | 120 0 1 1 1 1 0 0 1 | 121 0 1 1 1 1 0 1 0 | 122 0 1 1 1 1 0 1 1 | 123 0 1 1 1 1 1 0 0 | 124 0 1 1 1 1 1 0 1 | 125 0 1 1 1 1 1 1 0 | 126 0 1 1 1 1 1 1 1 | 127 1 0 0 0 0 0 0 0 | 128 1 0 0 0 0 0 0 1 | 129 1 0 0 0 0 0 1 0 | 130 1 0 0 0 0 0 1 1 | 131 1 0 0 0 0 1 0 0 | 132 1 0 0 0 0 1 0 1 | 133 1 0 0 0 0 1 1 0 | 134 1 0 0 0 0 1 1 1 | 135 1 0 0 0 1 0 0 0 | 136 1 0 0 0 1 0 0 1 | 137 1 0 0 0 1 0 1 0 | 138 1 0 0 0 1 0 1 1 | 139 1 0 0 0 1 1 0 0 | 140 1 0 0 0 1 1 0 1 | 141 1 0 0 0 1 1 1 0 | 142 1 0 0 0 1 1 1 1 | 143 1 0 0 1 0 0 0 0 | 144 1 0 0 1 0 0 0 1 | 145 1 0 0 1 0 0 1 0 | 146 1 0 0 1 0 0 1 1 | 147 1 0 0 1 0 1 0 0 | 148 1 0 0 1 0 1 0 1 | 149 1 0 0 1 0 1 1 0 | 150 1 0 0 1 0 1 1 1 | 151 1 0 0 1 1 0 0 0 | 152 1 0 0 1 1 0 0 1 | 153 1 0 0 1 1 0 1 0 | 154 1 0 0 1 1 0 1 1 | 155 1 0 0 1 1 1 0 0 | 156 1 0 0 1 1 1 0 1 | 157 1 0 0 1 1 1 1 0 | 158 1 0 0 1 1 1 1 1 | 159 1 0 1 0 0 0 0 0 | 160 1 0 1 0 0 0 0 1 | 161 1 0 1 0 0 0 1 0 | 162 1 0 1 0 0 0 1 1 | 163 1 0 1 0 0 1 0 0 | 164 1 0 1 0 0 1 0 1 | 165 1 0 1 0 0 1 1 0 | 166 1 0 1 0 0 1 1 1 | 167 1 0 1 0 1 0 0 0 | 168 1 0 1 0 1 0 0 1 | 169 1 0 1 0 1 0 1 0 | 170 1 0 1 0 1 0 1 1 | 171 1 0 1 0 1 1 0 0 | 172 1 0 1 0 1 1 0 1 | 173 1 0 1 0 1 1 1 0 | 174 1 0 1 0 1 1 1 1 | 175 1 0 1 1 0 0 0 0 | 176 1 0 1 1 0 0 0 1 | 177 1 0 1 1 0 0 1 0 | 178 1 0 1 1 0 0 1 1 | 179 1 0 1 1 0 1 0 0 | 180 1 0 1 1 0 1 0 1 | 181 1 0 1 1 0 1 1 0 | 182 1 0 1 1 0 1 1 1 | 183 1 0 1 1 1 0 0 0 | 184 1 0 1 1 1 0 0 1 | 185 1 0 1 1 1 0 1 0 | 186 1 0 1 1 1 0 1 1 | 187 1 0 1 1 1 1 0 0 | 188 1 0 1 1 1 1 0 1 | 189 1 0 1 1 1 1 1 0 | 190 1 0 1 1 1 1 1 1 | 191 1 1 0 0 0 0 0 0 | 192 1 1 0 0 0 0 0 1 | 193 1 1 0 0 0 0 1 0 | 194 1 1 0 0 0 0 1 1 | 195 1 1 0 0 0 1 0 0 | 196 1 1 0 0 0 1 0 1 | 197 1 1 0 0 0 1 1 0 | 198 1 1 0 0 0 1 1 1 | 199 1 1 0 0 1 0 0 0 | 200 1 1 0 0 1 0 0 1 | 201 1 1 0 0 1 0 1 0 | 202 1 1 0 0 1 0 1 1 | 203 1 1 0 0 1 1 0 0 | 204 1 1 0 0 1 1 0 1 | 205 1 1 0 0 1 1 1 0 | 206 1 1 0 0 1 1 1 1 | 207 1 1 0 1 0 0 0 0 | 208 1 1 0 1 0 0 0 1 | 209 1 1 0 1 0 0 1 0 | 210 1 1 0 1 0 0 1 1 | 211 1 1 0 1 0 1 0 0 | 212 1 1 0 1 0 1 0 1 | 213 1 1 0 1 0 1 1 0 | 214 1 1 0 1 0 1 1 1 | 215 1 1 0 1 1 0 0 0 | 216 1 1 0 1 1 0 0 1 | 217 1 1 0 1 1 0 1 0 | 218 1 1 0 1 1 0 1 1 | 219 1 1 0 1 1 1 0 0 | 220 1 1 0 1 1 1 0 1 | 221 1 1 0 1 1 1 1 0 | 222 1 1 0 1 1 1 1 1 | 223 1 1 1 0 0 0 0 0 | 224 1 1 1 0 0 0 0 1 | 225 1 1 1 0 0 0 1 0 | 226 1 1 1 0 0 0 1 1 | 227 1 1 1 0 0 1 0 0 | 228 1 1 1 0 0 1 0 1 | 229 1 1 1 0 0 1 1 0 | 230 1 1 1 0 0 1 1 1 | 231 1 1 1 0 1 0 0 0 | 232 1 1 1 0 1 0 0 1 | 233 1 1 1 0 1 0 1 0 | 234 1 1 1 0 1 0 1 1 | 235 1 1 1 0 1 1 0 0 | 236 1 1 1 0 1 1 0 1 | 237 1 1 1 0 1 1 1 0 | 238 1 1 1 0 1 1 1 1 | 239 1 1 1 1 0 0 0 0 | 240 1 1 1 1 0 0 0 1 | 241 1 1 1 1 0 0 1 0 | 242 1 1 1 1 0 0 1 1 | 243 1 1 1 1 0 1 0 0 | 244 1 1 1 1 0 1 0 1 | 245 1 1 1 1 0 1 1 0 | 246 1 1 1 1 0 1 1 1 | 247 1 1 1 1 1 0 0 0 | 248 1 1 1 1 1 0 0 1 | 249 1 1 1 1 1 0 1 0 | 250 1 1 1 1 1 0 1 1 | 251 1 1 1 1 1 1 0 0 | 252 1 1 1 1 1 1 0 1 | 253 1 1 1 1 1 1 1 0 | 254 1 1 1 1 1 1 1 1 | 255