{"id":201,"date":"2014-11-02T18:20:22","date_gmt":"2014-11-02T18:20:22","guid":{"rendered":"https:\/\/projects.lsv.ens-paris-saclay.fr\/orchidsdev\/?p=201"},"modified":"2014-11-05T16:34:25","modified_gmt":"2014-11-05T16:34:25","slug":"strange-behaviors-with-characters","status":"publish","type":"post","link":"https:\/\/projects.lsv.ens-paris-saclay.fr\/orchidsdev\/?p=201","title":{"rendered":"Strange behaviors with characters"},"content":{"rendered":"

Some functions in the C code of Orchids use objects of type char<\/code>, some others of type unsigned char<\/code>. You will sometimes see strange sequences of casts in the code of Orchids, such as:<\/p>\n

{\r\n  unsigned char c;\r\n\r\n  \/* ... *\/\r\n  switch ((int)(unsigned int)c) {\r\n    \/* ... *\/\r\n  }\r\n}\r\n<\/pre>\n
To understand what is at stake, consider the following piece of code:<\/p>\n
{\r\n  char c;\r\n\r\n  switch (c) {\r\n    \/* ... *\/\r\n    case '\u00e9': return 'e';\r\n    case '\u00e0': return 'a';\r\n    \/* ... *\/\r\n    default: return c;\r\n  }\r\n}\r\n<\/pre>\n
This appears to be some code whose purpose would be to remove accents from letters, but is completely buggy.<\/p>\n
One reason is that we accented characters such as '\u00e9'<\/code> or '\u00e0'<\/code> are system and compiler-dependent constants (more precisely, everything depends on the chosen character encoding<\/a>), and should not be used as such.<\/p>\n
However, the reason why I am giving that code as an example is to show an example of a very strange bug with characters in C.<\/p>\n
It is very likely that, if you start with code with '\u00e9'<\/code> in c<\/code>, it will not<\/em> return 'e'<\/code>.<\/p>\n
Let me give the basic reasons for this strange behavior:<\/p>\n