C++: 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 - please doublecheck if this is correct (and for sure not the best/fastest way of doing it).
1) 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;
- };
-
2) Now declare the variables in the function you're using:
- void myfunction()
- {
- char cTarget;
- BITS b;
-
3) 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);
-
4) 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 altogether:
- 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