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.NET Forum / Languages / Managed C++ / June 2005Problems working with strings in MC++
Being an old MFC guy, I'm having a heck of a time working with MC++. Can anybody tell me why the following code outputs 65 instead of an A. And yes I know 65 is the hex value for A, but why is it getting converted? And how to I get an A to be outputted? char c = 'A'; StringBuilder *s = new StringBuilder; s->Append(c); Console::WriteLine(s); Thanks JEK > Being an old MFC guy, I'm having a heck of a time working with MC++. Can > anybody tell me why the following code outputs 65 instead of an [quoted text clipped - 5 lines] > s->Append(c); > Console::WriteLine(s); Because char maps to System.UInt8, not System.Char. Try wchar_t c = L'A'; StringBuilder *s = new StringBuilder; s->Append(c); Console::WriteLine(s); -cd >> Being an old MFC guy, I'm having a heck of a time working with MC++. Can >> anybody tell me why the following code outputs 65 instead of an [quoted text clipped - 16 lines] > > -cd Sorry Carl, No help; This is a simple fragment of the real sitiuation. The <char c> is really being returned from a COM object, therefore it cannot be defined as anything other than a char. BTW, your code also yields 65. JEK >> Being an old MFC guy, I'm having a heck of a time working with MC++. Considering that ordinary C++ predates MFC (though the C++ standard doesn't), some of us who saw C++ learn how to choose overloads depending on char vs. int also wonder why MC++ lacks that ability. Anyway... >> Can anybody tell me why the following code outputs 65 instead of an A. >> And yes I know 65 is the hex Decimal. Hex is 0x41. >> char c = 'A'; >> StringBuilder *s = new StringBuilder; >> s->Append(c); >> Console::WriteLine(s); > > Because char maps to System.UInt8, not System.Char. Last I saw, char maps to System.Int8 or System.Byte or something like that. Of course C programmers have to take care not to depend on whether char's values are signed or unsigned, but MC++ programmers often have to find out which MC++ type is actually being used. > Try > > wchar_t c = L'A'; > StringBuilder *s = new StringBuilder; > s->Append(c); > Console::WriteLine(s); wchar_t maps onto System.UInt16. Try: char c = 'A'; // or wchar_t c = L'A'; /// or _TCHAR c = _T('A'); StringBuilder *s = new StringBuilder; s->Append(Char(c)); Console::WriteLine(s); I'm not actually sure if this will work. Char('A') worked for me but I didn't try it with a variable. Char('\0') has a minor bug but works OK at execution time. >>> Being an old MFC guy, I'm having a heck of a time working with MC++. > [quoted text clipped - 38 lines] > didn't try it with a variable. Char('\0') has a minor bug but works OK at > execution time. Hi Norman, Char c = 'A' instead of char = 'A' works... Thanks JEK Hi Carl, > Because char maps to System.UInt8, not System.Char. > [quoted text clipped - 4 lines] > s->Append(c); > Console::WriteLine(s); Last I remember, that will only work if compiling with /Zc:wchar_t, because otherwise, wchar_t maps to UInt16 :)  SignatureTomas Restrepo tomasr@mvps.org http://www.winterdom.com/ Tomas Restrepo (MVP) wrote: > Hi Carl, > [quoted text clipped - 9 lines] > Last I remember, that will only work if compiling with /Zc:wchar_t, > because otherwise, wchar_t maps to UInt16 :) No doubt. I take it for granted since /Zc:wchar_t is the default in VC 2005. -cd > Being an old MFC guy, I'm having a heck of a time working with MC++. Can > anybody tell me why the following code outputs 65 instead of an A... [quoted text clipped - 3 lines] > s->Append(c); > Console::WriteLine(s); This is my guess... http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlr fsystemtextstringbuilderclassappendtopic11.asp SignatureJeff Partch [VC++ MVP] >> Being an old MFC guy, I'm having a heck of a time working with MC++. Can >> anybody tell me why the following code outputs 65 instead of an A... [quoted text clipped - 6 lines] > This is my guess... > http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlr fsystemtextstringbuilderclassappendtopic11.asp Thanks Jeff, that's the answer.. Use Char c = 'A' instead char c = 'A'.. What's interesting is char c = 'A' works in C# Go figure... JEK > Thanks Jeff, that's the answer.. > > Use Char c = 'A' instead char c = 'A'.. > > What's interesting is char c = 'A' works in C# char is a keyword in both C++ and C#. In C++, char is defined as a single byte (the smallest addressible unit of storage). In .NET, this maps to System.UInt8, while in C#, char is defined as the "platform character type", or System.Char. Char, on the other hand, is not a keyword/built-in, but the name of a value type in the System namespace, so it has the same meaning in both languages. The solution of declaring variables of type Char won't help your case of getting character data from a COM object or other legacy code that's returning character strings using the C/C++ char type. You can get away with a cast to convert a single char to Char, but to convert strings, you'll want to use the functions in the System.Runtime.InteropServices.Marshal class. Specifically, you might want to read up on: StringToHGlobalAnsi StringToHGlobalUni StringToHGlobalAuto StringToBSTR PtrToStringAuto PtrToStringAnsi PtrToStringUni PtrToStringBSTR -cd >> Thanks Jeff, that's the answer.. >> [quoted text clipped - 29 lines] > > -cd What about a struct and a pointer to a struct that is returned by a COM object. What is the best handle them in manaaged code? JEK > What about a struct and a pointer to a struct that is returned by a > COM object. What is the best handle them in manaaged code? One of the great advantages of MC++ is that you can just use unmanaged types freely. If you need to pass a native struct to a framework library, or some other existing IL code (i.e. not MC++ code that you're writing), then you either need to define a managed equivalent and copy the struct over member by member (possibly doing string conversions on the way), or you may be able to define a managed struct that's layout compatible with the unmanaged struct by using explicit layout attributes on the managed struct. -cd Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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