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ABENUNICODE_OVERVIEW - UNICODE OVERVIEW

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Unicode - Overview

Character Sets

Application Server ABAP supports both Unicode and non-Unicode systems. Non-Unicode systems are ABAP systems in which one character is usually represented by one byte. Unicode systems are ABAP systems that are based on a Unicode character format and an appropriate operating system and database.

Before Unicode, SAP used various different codes for representing characters in different fonts, such as ASCII, EBCDIC as single-byte code pages, or double-byte code pages:

• ASCII (American Standard Code for Information Interchange) encodes every character with one byte. This means that a maximum of 256 characters can be displayed (strictly speaking, standard ASCII only encodes one character using 7 bit and can therefore only represent 128 characters. The extension to 8 bit is introduced with ISO-8859). Examples of common code pages are ISO-8859-1 for Western European, or ISO-8859-5 for Cyrillic fonts.

• EBCDIC (Extended Binary Coded Decimal Interchange) also encodes each character using one byte, and can therefore also represent 256 characters. For example, EBCDIC 0697/0500 is an IBM format that has been used on the AS/400 platform (now known as IBM System i) for Western European fonts.

• Double byte code pages require between 1 and 2 bytes per character. This enables the representation of 65,536 characters, of which only 10,000 to 15,000 characters are normally used. For example, the code page SJIS is used for Japanese and BIG5 for traditional Chinese fonts.

Using these character sets, all languages can be handled individually in one AS ABAP. Difficulties arise if texts from different incompatible character sets are mixed in one central system. The exchange of data between systems with incompatible character sets can also lead to problems.

The solution to this problem is the use of a character set that includes all characters at once. This is realized by Unicode (ISO/IEC 10646) with the character set UCS. A variety of Unicode character formats is possible for the Unicode character set, for example UTF, in which a character can occupy between one and four bytes or UCS-2, where a character occupies two bytes. The system code page of a Unicode system is UTF-16 and the programming language supports the character format UCS-2. This mostly matches the UTF-16 format and includes all its characters except for those from the surrogate area. A restriction to UCS-2 means that a character is always assumed as having a length of two bytes. This generally only produces problems if character strings are truncated in the middle of a character representation or if individual characters from sets of characters are compared in character string processing.

Using Unicode offers the following benefits:

• A single Unicode system can cover all business processes in all countries concerned.

• Data can be transferred between different Unicode systems without loss of information.

• Unicode systems can show more than one language at once on a single user interface.

Switching to Unicode

Before Unicode support was introduced, many ABAP programmers assumed that one character corresponded to one byte. Before a non-Unicode system is converted to Unicode, therefore, ABAP programs must be changed wherever an explicit or implicit assumption is made about the internal length of a character. This mainly affects

• character and byte string processing (of course)

• access to structures. The latter case applies since flat structures in non-Unicode programs are handled like character-like data objects and some programming techniques exploit this fact. The Unicode fragment view was introduced to enable the handling of structures.

ABAP supports this conversion using new syntax rules and new language constructs, whereby emphasis was placed on retaining as much of the existing source code as possible. As a preparation for the conversion to Unicode - but also independently of whether a system will actually be converted to Unicode - the checkbox Unicode checks active can be selected in the program properties. The transaction UCCHECK supports the activation of this check for existing programs. If this property is set, the program is identified as a Unicode program. In a Unicode program, an additional stricter syntax check is performed than in non-Unicode programs. In some cases, statements must also be enhanced by using new additions. A syntactically correct Unicode program will normally run with the same semantics and the same results in Unicode and non-Unicode systems. (Exceptions to this rule are low-level programs that query and evaluate the number of bytes per character.) Programs that are required to run in both systems should therefore also be tested on both platforms.

In a Unicode system, only Unicode programs can be executed. Before converting to a Unicode system, the profile parameter abap/unicode_check should be set to "ON" so that only the execution of Unicode programs is permitted. Non-Unicode programs can only be executed in non-Unicode systems. All language constructs that have been introduced for Unicode programs can, however, also be used in non-Unicode programs.

It has been established that existing programs that have been programmed with no errors mostly fulfill the new Unicode rules and therefore require very little modification. Conversely, most programs that require significant changes are due to an error-prone and therefore questionable programming style. Even if planning a conversion to a Unicode system is not planned, Unicode programs are preferable because they are more easily maintained and less prone to errors. Just as outdated and dangerous language constructs are declared obsolete and are no longer permitted for use in ABAP Objects, the rules for Unicode programs also offer increased security when programming, for example when working with character fields and mixed structures. This applies particularly for the storage of external data (for example using the file interface), which has been completely reviewed for use in Unicode programs. When creating a new program, SAP therefore recommends that the program is always identified as a Unicode program; older programs can be converted to Unicode in stages.

Notes

• The program RSUNISCAN_FINAL can be used instead of transaction UCCHECK.

• A Unicode program with correct syntax must be checked for functional correctness in Unicode systems (and possibly also in non-Unicode systems). This can be done using unit tests from ABAP UNIT and associated test coverage checks from Coverage Analyzer.

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