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I am currently working on creating an OpenSource version of
the XarLib library (see http://www.xara.com/support/docs/webformat/spec/)
that will build on Linux, Mac and Windows. This library really needs to
build in both Unicode and non-unicode versions and shouldn’t require
wxWidgets. The library consists of the Xar format loading and saving code
from XaraLX with a small wrapper around it providing a simple interface. While
trying to update some of the XaraLX files from the latest version I have come
across several problems that really need to be sorted out properly… Use of _T(), # and ## I went into this in my message of 29/03 but I’ve
looked into it a bit more and the MS compiler errors if you try to concatenate
a narrow and a wide string. Gcc behaves differently e.g.: char testa[256] = "Hello" "world"; char testb[256] = "Hello" L"world"; char testc[256] = L"Hello" "world"; char testd[256] = L"Hello" L"world"; wchar_t wtesta[256] = "Hello" "world"; wchar_t wtestb[256] = "Hello" L"world"; wchar_t wtestc[256] = L"Hello" "world"; wchar_t wtestd[256] = L"Hello" L"world"; TCHAR ttesta[256] = "Hello" "world"; TCHAR ttestb[256] = "Hello" L"world"; TCHAR ttestc[256] = L"Hello" "world"; TCHAR ttestd[256] = L"Hello" L"world"; MSVC gives the following errors (in a Unicode build): (2) : error C2308: concatenating mismatched wide strings (3) : error C2308: concatenating mismatched wide strings (3) : error C2440: 'initializing' : cannot convert from
'const unsigned short [8]' to 'char [256]' There is no
context in which this conversion is possible (4) : error C2440: 'initializing' : cannot convert from
'const unsigned short [11]' to 'char [256]' There is no
context in which this conversion is possible (5) : error C2440: 'initializing' : cannot convert from
'const char [11]' to 'wchar_t [256]' There is no
context in which this conversion is possible (6) : error C2308: concatenating mismatched wide strings (6) : error C2440: 'initializing' : cannot convert from
'const char [17]' to 'wchar_t [256]' There is no
context in which this conversion is possible (7) : error C2308: concatenating mismatched wide strings (9) : error C2440: 'initializing' : cannot convert from
'const char [11]' to ‘TCHAR [256]' There is no
context in which this conversion is possible (10) : error C2308: concatenating mismatched wide strings (10) : error C2440: 'initializing' : cannot convert from
'const char [17]' to 'TCHAR [256]' There is no
context in which this conversion is possible (11) : error C2308: concatenating mismatched wide strings Concatenation of the mismatched strings gives an error but
then continues compilation using the type of the first sub-string. GCC gives the following: 2:error: char-array initialised from wide string 3:error: char-array initialised from wide string 4:error: char-array initialised from wide string 5:error: int-array initialised from non-wide string 9:error: int-array initialised from non-wide string Also, removing the lines that error shows that the other
lines all produce a fully wide string (e.g. lines 10, 11 and 12 all produce a
TCHAR string saying “Helloworld”. So, it appears that when concatenating strings, if any of
the sub-strings are wide then gcc promotes all of the substrings to wide ones.
This explains why our macros that do this compile on linux but not on MSVC. Use of %s in C runtime printf type functions It appears as though on linux %s always means a narrow char
string even in the wide version of the function. To pass a wide string
you must specify %ls. However, on windows, MS have “helpfully”
changed the wide string version (e.g. swprintf) so that %s means a TCHAR
pointer and to force a narrow string you have to use %hs (you can still use %ls
to force a wide string). This can be handled by the PERCENT_S macro (with
new PERCENT_Sa and PERCENT_Sw macros for forcing to narrow or wide) but there
are quite a lot of calls to printf type functions that pass a %s that need to
be changed to work correctly (e.g. at present they will not work correctly on
linux because they use %s but pass a TCHAR*). Also there are quite a few
places where narrow strings are used deliberately and this requires that the
PERCENT_S macros are not used (as they are defined as wide strings on Unicode builds). Other printf type functions XaraLX also implements some of its own printf type
functions, _MakeMsg, CCvsprintf etc. These only handle a subset of the
standard % codes and all treat %s as a TCHAR* and don’t allow the use of different
width strings. Other problematic string usage There are various places in the XaraLX code where narrow
string functions are specifically used but are passed TCHAR* as parameters.
Presumably this sort of thing is being fixed when the files are initially
ported. I think the best solution for this would be for all of our
printf type functions to behave the same and preferably not require the use of
PERCENT_S type macros but this would involve updating our own functions (e.g. to
support floating point) and also making the standard printf type functions on
linux treat %s as TCHAR* (either by a wrapper that rewrites the format string
or by writing our own version). Alternatively, we would have to carefully
document exactly what each does support and document how they must be used to
be portable. Gerry |