How to convert AnsiString to std::string in C++ Builder?

Question

I would like to ask how can I get a text input from TEdit control and cast it to std::string (not AnsiString).

For example, if I have a TEdit control with the name User, I get the text from it with the User->Text command. What I want to do is to assign that value to a std::string, for example string my_str = User->Text;.

I would like to ask, how can I do this in C++ Builder? Is there some sort of a ToString() method or sort of, because I was not able to find one.

Answer 1

In C++Builder 2007 and earlier, TEdit::Text is an 8-bit AnsiString in the user's default ANSI locale. It is very straight forward to convert an AnsiString to a std::string - just use the AnsiString::c_str() method to get a null-terminated char* pointer to the AnsiString data, and then you can assign that to the std::string, eg:

std::string my_str = User->Text.c_str();
/* or:
System::AnsiSystem text = User->Text;
std::string my_str(text.c_str(), text.Length());
*/

If you want the std::string data to be in another character encoding, such as UTF-8, then you will have to convert the AnsiString data accordingly, such as with MultiByteToWideChar()/WideCharToMultiByte(), UTF8Encode(), etc, before assigning it to the std::string.

---

In C++Builder 2009 and later, TEdit::Text is a 16-bit UnicodeString in UTF-16 format. The easiest way to convert a UnicodeString to a std::string is to first convert to an AnsiStringT<CP> (where CP is the desired ANSI codepage - AnsiString uses CP=0, UTF8String uses CP=65001, etc), and then convert that to std::string, eg:

std::string my_str = AnsiString(User->Text).c_str(); // or UTF8String, etc...
/* or:
System::AnsiString text = User->Text; // or UTF8String, etc...
std::string my_str(text.c_str(), text.Length());
*/

Alternatively, in C++11 and later, you can convert the UnicodeString to a std::wstring first, and then use std::wstring_convert, eg:

#include <locale>

std::wstring my_wstr = User->Text.c_str();
/* or:
System::UnicodeString text = User->Text;
std::wstring my_wstr(text.c_str(), text.Length());
*/

// System::Char may be either wchar_t or char16_t, depending
// on which platform you are compiling for...
std::string my_str = std::wstring_convert<std::codecvt_utf8_utf16<System::Char>>{}.to_bytes(my_wstr);

Answer 2

I had a lot of those to migrate from Borland to Embarcadero Rio. So I created a method to do it.

#include <cwchar.h>   //std::wcslen

char* __fastcall AnsiOf(wchar_t* w)
{
 static char c[STR_CONV_BUF_SIZE];
 memset(c, 0, sizeof(c));
 WideCharToMultiByte(CP_ACP, WC_NO_BEST_FIT_CHARS, w, std::wcslen(w), c, STR_CONV_BUF_SIZE, NULL, NULL);
 return c;
}

std::string my_str = AnsiOf((User->Text).c_str());