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File Interfaces and Unicode

As the content of files often reflects the structure of data in the working memory, the file interface in a Unicode system must be able to cope with the following demands:

  • It must be possible to exchange files between Unicode and non-Unicode systems.
  • It must be possible to exchange files between different Unicode systems.
  • It must be possible to exchange files between different non-Unicode systems that work with different code pages.

    • For this reason, in Unicode programs you must always declare according to which codepage character type the data that is written in or is read from text files text file is coded.

    You must also take into account that a Unicode program must be executable in both Unicode and non-Unicode systems. Some syntax rules have therefore been changed for the file interface in such a way that the programming of file accessing in Unicode programs is less error-prone than in non-Unicode programs.

  • A file must be explicitly opened before every read or write operation. An open file cannot be opened again. In non-Unicode programs, the first time a file is implicitly opened, it is opened with the default settings. The statement to open a file in non-Unicode programs can be used on files which are already open, although it is not possible to open a file more than once in the same program.
  • The type of access and data storage must be explicitly specified when a file is opened. In non-Unicode systems, a file is opened with the implicit default settings if no other settings are specified.
  • When a file is opened to read its content, it is only possible to read from this file. In non-Unicode programs, it is also possible to write to files which have been opened in this way.
  • When a file is opened as text file, only the content of character-type data objects can be read or written to. In non-Unicode systems, numerical and byte-type data objects may also be accessed.

    • Normally explicit programming is required, where all important parameters must be entered, rather than programming with default settings, over which the developer has no influnce. Furthermore, error-prone mixed forms of byte-type, character-type, and numerical data is not allowed.

    For this reason, it is sensible to keep to the syntax rules for Unicode programs when using the file interface, even if the system itself is non-Unicode.

    Other versions: 7.31 | 7.40 | 7.54