How can I use fprintf to write text from a TEdit control to a file in C++Builder 10.1

Question

I'm pretty sure this worked in an earlier version of C++Builder but now I need to figure out the easiest way to get this to work in C++Builder 10.1.

fprintf(out, "%s\n", Edit1->Text);

I have no idea why, but right now it seems to be writing only the first character of the text in Edit1 to the file.

Also if anyone has a link to a good source for best practices for dealing with strings C++Builder 10.1, I would be grateful.

Answer 1

After some more reading it seems the solution is pretty easy.

fwprintf(out, L"%s\n", Edit1->Text);

What I find most odd is, as near as I can tell, the Text property doesn't have a type. How are you supposed to know work with it when it has no type?

Answer 2

I'm pretty sure this worked in an earlier version of C++Builder

Maybe, but only in pre-CB2009 versions, where the Text was an AnsiString (since CB2009, it is now a UnicodeString), and only as a fluke of undefined behavior, since you can't pass an (Ansi|Unicode)String object to fprintf() to begin with, it expects a pointer to a C-style character string instead. The sole data member of an AnsiString is a char*, and the sole data member of a UnicodeString is a wchar_t*/char16_t* on Windows/Posix (respectively).

now I need to figure out the easiest way to get this to work in C++Builder 10.1.

You have a few choices:

• cast the Text to an AnsiString and then use its c_str() method to get a char* pointer:

  fprintf(out, "%s\n", AnsiString(Edit1->Text).c_str());

• use fprintf() with the %Ls placeholder instead:

  fprintf(out, "%ls\n", Edit1->Text.c_str());

• use fwprintf() instead:

  fwprintf(out, L"%s\n", Edit1->Text.c_str());

• use a more modern file I/O library, like the standard C++ std::ofstream, or the RTL's TStreaWriter, etc.

I have no idea why, but right now it seems to be writing only the first character of the text in Edit1 to the file.

Because you are telling fprintf() (via %s) to expect an 8bit null-terminated char* string, but you are passing it a 16bit wchar_t* string instead. ASCII characters have 0x00 bytes in them in 16bit strings.

Also if anyone has a link to a good source for best practices for dealing with strings C++Builder 10.1, I would be grateful.

Have you read Embarcadero's Migration and Upgrade documentation yet? It has a section on migrating ANSI code to Unicode.