Tham khảo tài liệu 'the new c standard- p4', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Character sets 223 Table Relative frequency most common to least common with parenthesis used to bracket extremely rare letters of letter usage in various human languages the English ranking is based on the British National Corpus . Based on Kelk. 729 Language Letters English French Norwegian Swedish Icelandic Hungarian etaoinsrhldcumfpgwybvkxjqz esaitnrulodcmpevqfbghjaxeyezagiuouikew erntsilakodgmvfupbhajyafficwzx q eantrsildomkgvafhupaobcyjxwzeq anriestublgmkfhvoapidjobyffiuopeycxwzq eatlnskomzrigaeydbvhjofupd6cuiuuxw q 222 The representation of each member of the source and execution basic character sets shall fit in a byte. Commentary This is a requirement on the implementation. The definition of character already specifies that it fits in a byte. However a character constant has type int which could be thought to imply that the value representation of characters need not fit in a byte. This wording clarifies the situation. The representation of members of the basic execution character set is also required to be a nonnegative value. A byte is at least large enough to contain any member of the basic execution character set and. . . basic character set fit in a byte 59 character single-byte 883 character constant type 478 basic character set positive if stored in char object This requirement reverses the dependency given in the C Standard but the effect is the same. Common Implementations On hosts where characters have a width 16 or 32 bits that choice has usually been made because of addressability issues pointers only being able to point at storage on 16- or 32-bit address boundaries . It is not usually necessary to increase the size of a byte because of representational issues to do with the character set. In the EBCDIC character set the value of a is 129 in Ascii it is 97 . If the implementation-defined value of CHAR_BIT is 8 then this character and some others will not be representable in the type signed 307 macro R-BIT char in most .