I have an LPCTSTR
and want to call a function that takes a std::string
parameter.
What conversion do I need to do?
The next method in this list to convert int to string in C++ is by using the to_string() function. This function is used to convert not only the integer but numerical values of any data type into a string. The to_string() method is included in the header file of the class string, i.e., <string> or <cstring>.
This LPCWSTR is Microsoft defined. So to use them we have to include Windows. h header file into our program. To convert std::wstring to wide character array type string, we can use the function called c_str() to make it C like string and point to wide character string.
An LPCSTR is a 32-bit pointer to a constant null-terminated string of 8-bit Windows (ANSI) characters.
Answers. LPCTSTR szTmp = _T("My String"); CString cszMyString(szTmp); // one way. CString cszMyString = szTmp; // another way.
LPCTSTR
can be either a single-byte or a multibyte string (depends on the UNICODE
constant being defined during compilation or not), while std::string
's users (including your function) normally use it to hold a single-byte string.
You 'd need two conversions: one for LPCSTR
(non-UNICODE
build) and one for LPCWSTR
(UNICODE
build). The first one is simple:
std::string convert(LPCSTR str) {
return std::string(str);
}
The second one needs its input parameter to be converted to another encoding first with WideCharToMultiByte
. Do not be alarmed by the name, the result can be a single-byte char string; that depends on the CodePage
parameter. You will have to use a codepage for a single-byte encoding, such as CP_ACP
.
Update: WideCharToMultiByte
example
Be aware that accurately converting to a single-byte encoding is technically impossible if the input string contains characters not existing in the target encoding's code page. Since you mention it's going to be for filesystem functions, if the file path contains such characters the conversion will not be 100% accurate and the subsequent function calls will fail.
std::string MBFromW(LPCWSTR pwsz, UINT cp) {
int cch = WideCharToMultiByte(cp, 0, pwsz, -1, 0, 0, NULL, NULL);
char* psz = new char[cch];
WideCharToMultiByte(cp, 0, pwsz, -1, psz, cch, NULL, NULL);
std::string st(psz);
delete[] psz;
return st;
}
Caveat emptor: The example above is from some code I had lying around and is not production-grade quality. The one immediately obvious flaw is that it is not exception-safe. It might also kill all the nice purple unicorns. Use it only as an example.
The naked truth is that std::string
can be used for multibyte encodings (such as UTF8) just fine -- you can even use it to hold wide-char strings, since it's just a binary-safe array of bytes at heart.
The problem is that the STL functions that apply to std::string
expect its contents to be in a single-byte encoding, and they won't produce correct results if this is not true.
By extension, we don't know what your function that takes an std::string
parameter expects -- it might expect a string encoded in UTF-8. But "by convention", I 'm assuming it also wants a single-byte-encoded string.
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