One of the C language’s strengths is that it can venture down into the depths of a computer’s inner workings. It loves to play in those dark, subterranean pools of raw data, bits, ports, and other primitive places that few high-level languages dare to tread.
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\nSpecifically, the C language is great at manipulating bit fields.<\/p>\n
A bit field<\/em> is where a byte, word, or larger chunk of data is manipulated one or more bits at a time. For example, an 8-bit byte (char<\/em>) may represent 8 different binary values or toggles. This approach is more efficient than using 8 separate int<\/em> variables to express on-off conditions.<\/p>\n You find bit fields used in legacy programs, dating back to when memory or storage was tight. Still, even when you have gigabytes available, sometimes packing a dozen or so conditions into a single int<\/em> makes sense. In the online world, bit fields are used frequently because it takes less time to transmit a 32-bit word than it does to transmit 32 words.<\/p>\n An example of a bit field is the way colors are mapped in computer graphics. Three colors — red, green, and blue — are represented by three bits:<\/p>\n As you run through the permutations of binary values When the red\/green\/blue bits combine, they create the intermediate colors, such as blue and green ( A fourth bit on the original PC ( The text color bit field on the original PC was 8-bits wide in total. The first four bits set the background color, the second four set the text color.<\/p>\n As an early PC programmer, I eventually committed the bit field values to memory. I still remember that PC text color is just one example of a bit field. In computerdom you’ll discover many bit fields. The C library uses bit fields in many functions and constants, but often macros are used to help manipulate them, so you don’t really get exposed directly. Regardless, bit fields allow for a lot of information to be contained in a tiny space.<\/p>\n As an example, suppose you’ve written a computer game. In the game, you use a bit field to track the status of a starship. The bit field looks like this:<\/p>\n Bit 0 – Transporter status Forgetting for a moment about Paramount Studios and their legions of lawyers defending copyrights, you need to code your game so that it can check the status of each of those bits, set a bit, and reset a bit. I’ll go over that process in next week’s Lesson<\/a>. Before then, here are some bit field tidbits to ponder:<\/p>\n Manipulate data at the lowest level. Continue reading 100<\/code> = Red
\n010<\/code> = Green
\n001<\/code> = Blue<\/p>\n001<\/code> through 111<\/code>, you encounter the basic PC text graphics colors, as shown in the table below.<\/p>\n\n
\n Binary<\/th>\n Hex\/Dec<\/th>\n Color<\/th>\n \n \n 000<\/td>\n 0x00 \/ 0<\/td>\n Black<\/td>\n<\/tr>\n \n 001<\/td>\n 0x01 \/ 1<\/td>\n Blue<\/td>\n<\/tr>\n \n 010<\/td>\n 0x02 \/ 2<\/td>\n Green<\/td>\n<\/tr>\n \n 011<\/td>\n 0x03 \/ 3<\/td>\n Cyan<\/td>\n<\/tr>\n \n 100<\/td>\n 0x04 \/ 4<\/td>\n Red<\/td>\n<\/tr>\n \n 101<\/td>\n 0x05 \/ 5<\/td>\n Magenta<\/td>\n<\/tr>\n \n 110<\/td>\n 0x06 \/ 6<\/td>\n Brown<\/td>\n<\/tr>\n \n 111<\/td>\n 0x07 \/ 7<\/td>\n White<\/td>\n<\/tr>\n<\/table>\n 011<\/code>) make cyan. Blue and red (101<\/code>) create magenta. All bits off (000<\/code>) is black. All bits on (111<\/code>) is white.<\/p>\n1000<\/code>) set color intensity. When that bit is on, a second set of 8 colors is available, from gray (1000<\/code> or “bright black”) through bright white (1111<\/code>). The color “bright brown” (1110<\/code>) is yellow.<\/p>\n0x04<\/code> is the text color red. In fact, the common acronym RGB helps me remember in which order the bits lie in the field: red, green, and blue.<\/p><\/blockquote>\n
\nBit 1 – Warp Drive
\nBit 2 – Shields
\nBit 3 – Phasers<\/p>\n\n