As with the floating-point numbers, the internal representation of characters
are also system-dependent. CHGLIB and CHKLIB are packages for standardizing
system-dependent character manipulation.
In FORTRAN grammar, the following FORTRAN character set is defined, and a program in FORTRAN must be written using only these characters. (Notes and contents of character-type data are exceptions to this rule.)
| Roman characters: | ABCDEFGHIJKLMNOPQRSTUVWXYZ |
| Numbers: | 0123456789 |
| Special characters: | blank'()*+,-./:= currency sign |
Therefore, strictly speaking, it is grammatically incorrect to write a
FORTRAN program using lower-case letters.
However, the method of internal representation of characters, including these FORTRAN characters, are not specifically defined in FORTRAN standard. As with the internal representation of floating-point numbers, there are two types of internal representation of characters: the EBCDIC of the IBM standard and the American standard code ASCII.
The Extended Binary Coded Decimal Interchange Code (EBCDIC) was set by IBM. True to its name, it is an extension of the BCD (binary coded decimal) code. The BCD code does not use the letters A, B, C, D, E , F for hexadecimals, and only uses the numbers 0-9 to represent decimal numbers. Four bits correspond to a single decimal digit.
A single word in EBCDIC is expressed by 8 bits. For numbers, the higher 4 bits correspond to F and the lower 4 bits to the BCD code. (Thus, it is called the EBCDIC.) This code is also implemented in the so-called IBM-compatible general-purpose machines such as Fujitsu and Hitachi, but there are subtle differences in the definition for each company.
Although all companies use the same code for FORTRAN characters, there are significant system dependencies regarding other characters. Especially, code systems are often changed to accommodate for the katakana used in Japanese. There are two main approaches to this. The first is to replace the lower-case letters in the alphabet with katakana. Of course, with this method, katakana and lower-case letters cannot be used simultaneously. This method is adopted by the Fujitsu M series (although conditions may differ among computer centers.) The other method replaces the lower-case letters with kanji, as in the first method, but also squeezes in the lower-case letters into empty codes. This is also called the EBCDIK code (the K standing for kana). This method is adopted by the Hitachi M series. Thus for these two methods, the upper-case alphabets and katakana will have the same codes, but the lower-case letters will not be interchangeable.
The ASCII code is a character code system that has been set by the American National Standards Institute (ANSII), and adopted by UNIX and MS-DOS. In Japan, the JIS X0201, which is almost the same as ASCII, is defined. The ASCII code is represented by 7 bits, with the highest digit begin 0. However, there exists a table of 8-bit codes that use all 8 bits to accommodate katakana in the JIS.
It can be seen that character codes are system dependent, even for FORTRAN
characters. Therefore, the ICHAR function that returns the character
code is a standard built-in function of FORTRAN, the returned value will be
system dependent. Functions LGE, LGT, LLE, LLT
are for comparing the values of the character code, free of any system
dependency. These functions compare the codes following the order of ASCII
codes, regardless of the code system used by the computer being used.
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | |
| 0 | NUL | DLE | SP | & | - | { | } | $ | 0 | |||||||
| 1 | SOH | DC1 | / | a | j | ~ |
A | J | 1 | |||||||
| 2 | STX | DC2 | FS | SYN | b | k | s | B | K | S | 2 | |||||
| 3 | ETX | DC3 | c | l | t | C | L | T | 3 | |||||||
| 4 | d | m | u | D | M | U | 4 | |||||||||
| 5 | HT | LF | e | n | v | E | N | V | 5 | |||||||
| 6 | BS | ETB | f | o | w | F | O | W | 6 | |||||||
| 7 | DEL | ESC | EOT | g | p | x | G | P | X | 7 | ||||||
| 8 | CAN | h | q | y | H | Q | Y | 8 | ||||||||
| 9 | EM | i | r | z | I | R | Z | 9 | ||||||||
| A | ※ | ※ | ※ | : | ||||||||||||
| B | VT | . | , | # | ||||||||||||
| C | FF | DC4 | < | * | % | @ | ||||||||||
| D | CR | GS | ENQ | NAK | ( | ) | _ | ' | ||||||||
| E | SO | RS | ACK | + | ; | > | = | |||||||||
| F | SI | US | BEL | SUB | ※ | ※ | ? | " |
\ (backslash).
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
| 0 | NUL | DLE | SP | 0 | @ | P | p | |
| 1 | SOH | DC1 | ! | 1 | A | Q | a | q |
| 2 | STX | DC2 | " | 2 | B | R | b | r |
| 3 | ETX | DC3 | # | 3 | C | S | c | s |
| 4 | EOT | DC4 | $ | 4 | D | T | d | t |
| 5 | ENQ | NAK | % | 5 | E | U | e | u |
| 6 | ACK | SYN | & | 6 | F | V | f | v |
| 7 | BEL | ETB | ' | 7 | G | W | g | w |
| 8 | BS | CAN | ( | 8 | H | X | h | x |
| 9 | HT | EM | ) | 9 | I | Y | i | y |
| A | LF | SUB | * | : | J | Z | j | z |
| B | VT | ESC | + | ; | K | [ | k | { |
| C | FF | FS | , | < | L | \ |
l | | |
| D | CR | GS | - | = | M | ] | m | } |
| E | SO | RS | . | > | N | ^ |
n | ~ |
| F | SI | US | / | ? | O | _ | o | DEL |
In JIS X0201, the \ and ~ in the above table become
/ and - (overline).
| Symbol | Name |
| NUL | null |
| SOH | start of heading |
| STX | start of text |
| ETX | end of text |
| EOT | end of transmission |
| ENQ | enquiry |
| ACK | acknowledge |
| BEL | bell |
| BS | backspace |
| HT | horizontal tabulation |
| LF | line feed |
| VT | horizontal tabulation |
| FF | form feed |
| CR | carriage return |
| SO | shift out |
| SI | shift in |
| DLE | data link escape |
| Symbol | Name |
| DC1 | device control 1 |
| DC2 | device control 2 |
| DC3 | device control 3 |
| DC4 | device control 4 |
| NAK | negative acknowledge |
| SYN | synchronous idle |
| ETB | end of transmission block |
| CAN | cancel |
| EM | end of medium |
| SUB | substitute character |
| ESC | escape |
| FS | file separator |
| GS | group separator |
| RS | record separator |
| US | unit separator |
| SP | space |
| DEL | delete |
| Code | Fujitsu | Hitachi | ASCII |
| 4A | c* | [ | [ |
| 4F | | |
! | ! |
| 5A | ! | ] | ] |
| 5B | \ | \ | $ |
| 5F | ¬ | ^ |
^ |
| 6A | | |
| |
|
| E0 | $ | $ | \ |
- Note 1: For Fujitsu, 4A is a c with a vertical bar.
- Note 2: The correspondence with the ASCII code is made for codes that are normally outputted at ASCII terminals, and it may be possible for the codes to be converted into codes not shown in the table.