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<< Click to Display Table of Contents >> Character sets |
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The shapes of characters that appear onscreen depend on an operating system's conventions for associating these shapes to internal binary values. Such conventions are called character sets, or code pages. The 8-bit code pages supported by BDE have 256 characters, numbered from 0 to 255 (using decimal values).
While most code pages use exactly the same numeric values (code points) for characters that are important in the United States, many of the symbols that are important to non-English-speaking countries map to different code points, depending on the particular code page. For example, the accented letter ‘á' maps to 160 on many DOS code pages, but in the Windows (ANSI) character set the same letter maps to code point 225. If an attempt is made to pass this character from an environment that uses the ANSI character set (used by most Windows programs) to a DOS environment, without translating the internal code point, the character appears under DOS as 'ß' (the German double-s) and may be misinterpreted in indexing, sorting, and so on. Character set identification and translation is therefore a very important issue if data loss is to be avoided internationally.
Characters whose code points are less than 128 are said to fall in the standard ASCII range; all the special international characters, located above code point 127, are known as extended characters.
BDE does not have a native character set. Usually, it operates with the binary values of characters. Strings should be passed to BDE in their default character set. The following table summarizes the default character sets for different character strings:.
Use |
For |
DOS code page |
Local file names and pathnames, local user names and database aliases, names for table lookup and referential integrity, non-maintained index names |
SQL server's character set |
SQL data and metadata (table, field and index names, passwords and user names) |
Table's character set |
Table field names, data, validity checks, and secondary and maintained index names |
ANSI |
All SQL scripts (for local or SQL tables) |
For QBE scripts, use the DOS character set for local table names and aliases. Use the ANSI character set for keywords and the table's character set for remaining characters in the script.
To translate character data between a table's native character set and Windows ANSI, use the functions DbiNativeToAnsi and DbiAnsiToNative. BDE returns error messages in the Windows ANSI character set.