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Character Facilities

The character data type differs from all the others in one important respect: every character item has a fixed length. This specifies the number of characters it holds.

The length of a literal character constant is just the number of characters between the enclosing apostrophes (except that two consecutive apostrophe within the string count as one). Thus:
is a character constant of length four. Because the length of every character variable, array, and function has to be specified in advance it is nearly always necessary to use CHARACTER statements to declare them, for example:
The same applies to named character constants but for these a special notation sets the length to that of the attached constant, which saves the trouble of counting characters:

      PARAMETER (TITLE = 'Latest mailing list')

The fixed length of character objects makes it easy to output data in a fixed format as when printing a table with neatly aligned columns, but sometimes it would be more convenient to have a variable length string type as some other languages do. The rules for character assignment go some way towards this: if an expression is too short then blanks are appended to it; if it is too long then characters are removed from the right-hand end. For many purposes, therefore, it is only necessary to ensure that character variables are at least as long as the longest string you need to store in them.

When transferring character information to procedures the length of the dummy argument can be set automatically to that of the corresponding actual argument. With this passed length notation it is easy to write general-purpose character handling procedures. This is described further in section 9.5.

The most common operations carried out on character strings are splitting them up and joining them together. Any section of a character variable or array element can be extracted by using the substring notation. Strings (and substrings) can be joined end to end by using the concatenation operator in a character expression. These are described in the next two sections.

Another fairly common requirement is to search for a particular sequence of characters within a longer string: this can be done with the intrinsic function INDEX.

Other intrinsic functions ICHAR and CHAR are provided to convert a single character to an integer or vice-versa according to its position within the native character set. More complicated conversions from a numerical data type to character form and vice-versa are best carried out using the internal file READ and WRITE statements which allow the power of the format specification to applied to the task. This mechanism is described in section 10.3.

Character strings can be compared to each other using relational operators or intrinsic functions. The latter use the ASCII collating sequence irrespective of the native character code. Further details are given in section 7.6.

next up previous contents index
Next: Character Substrings Up: Character Handling and Logic Previous: Character Handling and Logic
Helen Rowlands