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up vote 39 down vote favorite
16

CString is quite handy, while std::string is more compatible with STL container. I am using hash_map. However, hash_map does not support CString as key, so I want to convert CString into std::string.

Writing a CString hash function seems to take a lot of time.

CString -----> std::string

How can I do this?

std::string -----> CString:

inline CString toCString(std::string const& str)
{
    return CString(str.c_str()); 
}

Am I right?

EDIT:

Here are more questions:

How can I convert wstring, CString to each other?

//wstring -> CString,
std::wstring src;
CString result(src.c_str());
//CString->wstring. 
CString src;
::std::wstring des(src.GetString());

Is there any problem?

How can I convert std::wstring, std::string to each other?

share|improve this question
3  
I wouldn't do this... Using two different strings types is bad enough, but having to convert every time you do something with a map? Sounds terrible. Just be consistent and use std::string. If for some reason you really think CString is better, then define an hash function for it so your hash_map can use it, this is far better than doubling the confusing in your code. –  GManNickG Jul 12 '09 at 15:13
2  
Actually, If all code is written by myself it will be consistent, but there are some opensourced project such as freeimage sqlite used. I can not modify there code. –  user25749 Jul 13 '09 at 1:21

5 Answers 5

up vote 47 down vote accepted

According to CodeGuru:

CString to std::string:

CString cs("Hello");
std::string s((LPCTSTR)cs);

BUT: std::string cannot always construct from a LPCTSTR. i.e. the code will fail for UNICODE builds.

As std::string can construct only from LPSTR / LPCSTR, a programmer who uses VC++ 7.x or better can utilize conversion classes such as CT2CA as an intermediary.

CString cs ("Hello");
// Convert a TCHAR string to a LPCSTR
CT2CA pszConvertedAnsiString (cs);
// construct a std::string using the LPCSTR input
std::string strStd (pszConvertedAnsiString);

std::string to CString: (From Visual Studio's CString FAQs...)

std::string s("Hello");
CString cs(s.c_str());

CStringT can construct from both character or wide-character strings. i.e. It can convert from char* (i.e. LPSTR) or from wchar_t* (LPWSTR).

In other words, char-specialization (of CStringT) i.e. CStringA, wchar_t-specilization CStringW, and TCHAR-specialization CString can be constructed from either char or wide-character, null terminated (null-termination is very important here) string sources.
Althoug IInspectable amends the "null-termination" part in the comments:

NUL-termination is not required.
CStringT has conversion constructors that take an explicit length argument. This also means that you can construct CStringT objects from std::string objects with embedded NUL characters.

share|improve this answer
2  
Errr... you are welcome :) Thanks to Siddhartha Rao for the detailed explanations. –  VonC Nov 3 '08 at 7:15
    
The last paragraph is not entirely correct. NUL-termination is not required. CStringT has conversion constructors that take an explicit length argument. This also means that you can construct CStringT objects from std::string objects with embedded NUL characters. –  IInspectable Oct 28 '13 at 20:25
    
@IInspectable good point. I have included your comment in the answer for more visibility. –  VonC Oct 29 '13 at 6:43
up vote 2 down vote

It is more effecient to convert CString to std::string using the conversion where the length is specified.

CString someStr("Hello how are you");
std::string std(somStr, someStr.GetLength());

In tight loop this makes a significant performance improvement.

share|improve this answer
up vote -1 down vote

If you're looking to convert easily between other strings types, perhaps the _bstr_t class would be more appropriate? It supports converstion between char, wchar_t and BSTR.

share|improve this answer
1  
-1 CString already does all the conversions you name. And it did 3 years ago as well. No point in suggesting a type that is meant for use in COM environments. –  IInspectable Oct 28 '13 at 20:29
up vote 3 down vote

If you want something more C++-like, this is what I use. Although it depends on Boost, that's just for exceptions. You can easily remove those leaving it to depend only on the STL and the WideCharToMultiByte() Win32 API call.

#include <string>
#include <vector>
#include <cassert>
#include <exception>

#include <boost/system/system_error.hpp>
#include <boost/integer_traits.hpp>

/**
 * Convert a Windows wide string to a UTF-8 (multi-byte) string.
 */
std::string WideStringToUtf8String(const std::wstring& wide)
{
    if (wide.size() > boost::integer_traits<int>::const_max)
        throw std::length_error(
            "Wide string cannot be more than INT_MAX characters long.");
    if (wide.size() == 0)
        return "";

    // Calculate necessary buffer size
    int len = ::WideCharToMultiByte(
        CP_UTF8, 0, wide.c_str(), static_cast<int>(wide.size()), 
        NULL, 0, NULL, NULL);

    // Perform actual conversion
    if (len > 0)
    {
        std::vector<char> buffer(len);
        len = ::WideCharToMultiByte(
            CP_UTF8, 0, wide.c_str(), static_cast<int>(wide.size()),
            &buffer[0], static_cast<int>(buffer.size()), NULL, NULL);
        if (len > 0)
        {
            assert(len == static_cast<int>(buffer.size()));
            return std::string(&buffer[0], buffer.size());
        }
    }

    throw boost::system::system_error(
        ::GetLastError(), boost::system::system_category);
}
share|improve this answer
    
God another boost library reference... –  kelton52 Aug 19 '11 at 22:51
up vote 26 down vote

Solve that by using std::basic_string<TCHAR> instead of std::string and it should work fine regardless of your character setting.

share|improve this answer
2  
This method is more simple –  user25749 Feb 20 '09 at 3:04
4  
I like to typedef that for convenience and familiarity: typedef std::basic_string<TCHAR> tstring –  Mike Caron Feb 2 '12 at 18:02

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