How do you convert CString and std string std wstring to each other

Question

CString is quite handy  while std  string is more compatible with STL container  I am using hash map  However  hash map does not support CStrings as keys  so I want to convert the CString into a std  string  Writing a CString hash function seems to take a lot of time  CString ----- gt  std  string  How can I do this  std  string ----- gt  CString   inline CString toCString std  string const amp  str        return CString str c str         Am I right   EDIT  Here are more questions  How can I convert from wstring to CString and vice versa     wstring - gt  CString std  wstring src  CString result src c str         CString - gt  wstring CString src  std  wstring des src GetString      Is there any problem with this  Additionally  how can I convert from std  wstring to std  string and vice versa

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from this post  Thank you Mark Ransom    Convert CString to string  VC6   I have tested this and it works fine   std  string Utils  CString2String const CString amp  cString         std  string strStd       for  int i   0   i  lt  cString GetLength       i                if  cString i   lt   0x7f              strStd append 1  static cast lt char gt  cString i             else             strStd append 1                   return strStd

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This is a follow up to Sal s answer  where he she provided the solution   CString someStr  Hello how are you    std  string std somStr  someStr GetLength       This is useful also when converting a non-typical C-String to a std  string  A use case for me was having a pre-allocated char array  like C-String   but it s not NUL terminated   i e  SHA digest   The above syntax allows me to specify the length of the SHA digest of the char array so that std  string doesn t have to look for the terminating NUL char  which may or may not be there   Such as   unsigned char hashResult SHA DIGEST LENGTH       auto value   std  string reinterpret cast lt char  gt hashResult  SHA DIGEST LENGTH

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Solve that by using std  basic string lt TCHAR gt  instead of std  string and it should work fine regardless of your character setting

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One interesting approach is to cast CString to CStringA inside a string constructor  Unlike std  string s  LPCTSTR cs   this will work even if  UNICODE is defined  However  if that is the case  this will perform conversion from Unicode to ANSI  so it is unsafe for higher Unicode values beyond the ASCII character set  Such conversion is subject to the  CSTRING DISABLE NARROW WIDE CONVERSION preprocessor definition  https   msdn microsoft com en-us library 5bzxfsea aspx          CString s1  SomeString            string s2  CStringA s1

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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

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Works for me   std  wstring CStringToWString const CString amp  s        std  string s2      s2   std  string  LPCTSTR s       return std  wstring s2 begin   s2 end        CString WStringToCString std  wstring s        std  string s2      s2   std  string s begin   s end         return s2 c str

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Works for me   std  wstring CStringToWString const CString amp  s        std  string s2      s2   std  string  LPCTSTR s       return std  wstring s2 begin   s2 end        CString WStringToCString std  wstring s        std  string s2      s2   std  string s begin   s end         return s2 c str

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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

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Solve that by using std  basic string lt TCHAR gt  instead of std  string and it should work fine regardless of your character setting

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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

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Since VS2012    and at least until VS2017 v15 8 1   Since it s a MFC project  amp  CString is a MFC class  MS provides a Technical Note TN059  Using MFC MBCS Unicode Conversion Macros and Generic Conversion Macros   A2CW       LPCSTR   - gt   LPCWSTR    A2W        LPCSTR   - gt   LPWSTR    W2CA       LPCWSTR  - gt   LPCSTR    W2A        LPCWSTR  - gt   LPSTR      Use   void Example         UNICODE case          USES CONVERSION      1          CString to std  string   std  wstring     CString strMfc   Test        strMfc   L Test      std  string strStd   W2A strMfc         Conversion Macro  strStd    Test         std  wstring wstrStd   strMfc GetString       wsrStd   L Test          std  string to CString   std  wstring     strStd    Test 2       strMfc   strStd c str       strMfc   L Test 2      wstrStd   A2W strStd c str           Conversion Macro  wstrStd   L Test 2             std  wstring to CString   std  string      wstrStd   L Test 3       strMfc   wstrStd c str       strMfc   L Test 3      strStd   W2A wstrStd c str           Conversion Macro  strStd    Test 3         --  Footnotes    1  In order to for the conversion-macros to have space to store the temporary length  it is necessary to declare a local variable called  convert that does this in each function that uses the conversion macros  This is done by invoking the USES CONVERSION macro  In VS2017 MFC code  atlconv h  it looks like this    ifndef  DEBUG      define USES CONVERSION int  convert    convert   UINT  acp   ATL   AtlGetConversionACP     CP THREAD ACP      acp   LPCWSTR  lpw    lpw   LPCSTR  lpa    lpa   else      define USES CONVERSION int  convert   0    convert   UINT  acp   ATL   AtlGetConversionACP     CP THREAD ACP      acp   LPCWSTR  lpw   NULL    lpw   LPCSTR  lpa   NULL    lpa   endif

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Is there any problem    There are several issues    CString is a template specialization of CStringT  Depending on the BaseType describing the character type  there are two concrete specializations  CStringA  using char  and CStringW  using wchar t   While wchar t on Windows is ubiquitously used to store UTF-16 encoded code units  using char is ambiguous  The latter commonly stores ANSI encoded characters  but can also store ASCII  UTF-8  or even binary data  We don t know the character encoding  or even character type  of CString  which is controlled through the  UNICODE preprocessor symbol   making the question ambiguous  We also don t know the desired character encoding of std  string  Converting between Unicode and ANSI is inherently lossy  ANSI encoding can only represent a subset of the Unicode character set    To address these issues  I m going to assume that wchar t will store UTF-16 encoded code units  and char will hold UTF-8 octet sequences  That s the only reasonable choice you can make to ensure that source and destination strings retain the same information  without limiting the solution to a subset of the source or destination domains   The following implementations convert between CStringA CStringW and std  wstring std  string mapping from UTF-8 to UTF-16 and vice versa    include  lt string gt   include  lt atlconv h gt   std  string to utf8 CStringW const amp  src utf16        return   CW2A src utf16 GetString    CP UTF8  m psz       std  wstring to utf16 CStringA const amp  src utf8        return   CA2W src utf8 GetString    CP UTF8  m psz        The remaining two functions construct C   string objects from MFC strings  leaving the encoding unchanged  Note that while the previous functions cannot cope with embedded NUL characters  these functions are immune to that    include  lt string gt   include  lt atlconv h gt   std  string to std string CStringA const amp  src        return   src GetString    src GetString     src GetLength         std  wstring to std wstring CStringW const amp  src        return   src GetString    src GetString     src GetLength

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You can cast CString freely to const char  and then assign it to an std  string like this    CString cstring  MyCString    std  string str    const char  cstring

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from this post  Thank you Mark Ransom    Convert CString to string  VC6   I have tested this and it works fine   std  string Utils  CString2String const CString amp  cString         std  string strStd       for  int i   0   i  lt  cString GetLength       i                if  cString i   lt   0x7f              strStd append 1  static cast lt char gt  cString i             else             strStd append 1                   return strStd

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This works fine     Convert CString to std  string inline std  string to string const CString amp  cst        return CT2A cst GetString

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Since VS2012    and at least until VS2017 v15 8 1   Since it s a MFC project  amp  CString is a MFC class  MS provides a Technical Note TN059  Using MFC MBCS Unicode Conversion Macros and Generic Conversion Macros   A2CW       LPCSTR   - gt   LPCWSTR    A2W        LPCSTR   - gt   LPWSTR    W2CA       LPCWSTR  - gt   LPCSTR    W2A        LPCWSTR  - gt   LPSTR      Use   void Example         UNICODE case          USES CONVERSION      1          CString to std  string   std  wstring     CString strMfc   Test        strMfc   L Test      std  string strStd   W2A strMfc         Conversion Macro  strStd    Test         std  wstring wstrStd   strMfc GetString       wsrStd   L Test          std  string to CString   std  wstring     strStd    Test 2       strMfc   strStd c str       strMfc   L Test 2      wstrStd   A2W strStd c str           Conversion Macro  wstrStd   L Test 2             std  wstring to CString   std  string      wstrStd   L Test 3       strMfc   wstrStd c str       strMfc   L Test 3      strStd   W2A wstrStd c str           Conversion Macro  strStd    Test 3         --  Footnotes    1  In order to for the conversion-macros to have space to store the temporary length  it is necessary to declare a local variable called  convert that does this in each function that uses the conversion macros  This is done by invoking the USES CONVERSION macro  In VS2017 MFC code  atlconv h  it looks like this    ifndef  DEBUG      define USES CONVERSION int  convert    convert   UINT  acp   ATL   AtlGetConversionACP     CP THREAD ACP      acp   LPCWSTR  lpw    lpw   LPCSTR  lpa    lpa   else      define USES CONVERSION int  convert   0    convert   UINT  acp   ATL   AtlGetConversionACP     CP THREAD ACP      acp   LPCWSTR  lpw   NULL    lpw   LPCSTR  lpa   NULL    lpa   endif

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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  lt string gt   include  lt vector gt   include  lt cassert gt   include  lt exception gt    include  lt boost system system error hpp gt   include  lt boost integer traits hpp gt          Convert a Windows wide string to a UTF-8  multi-byte  string      std  string WideStringToUtf8String const std  wstring amp  wide        if  wide size    gt  boost  integer traits lt int gt   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 lt int gt  wide size              NULL  0  NULL  NULL           Perform actual conversion     if  len  gt  0                std  vector lt char gt  buffer len           len     WideCharToMultiByte              CP UTF8  0  wide c str    static cast lt int gt  wide size                  amp buffer 0   static cast lt int gt  buffer size     NULL  NULL           if  len  gt  0                        assert len    static cast lt int gt  buffer size                  return std  string  amp buffer 0   buffer size                          throw boost  system  system error            GetLastError    boost  system  system category

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You can use CT2CA   CString datasetPath  CT2CA st datasetPath   string dataset st

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Solve that by using std  basic string lt TCHAR gt  instead of std  string and it should work fine regardless of your character setting

User · Answer

This is a follow up to Sal s answer  where he she provided the solution   CString someStr  Hello how are you    std  string std somStr  someStr GetLength       This is useful also when converting a non-typical C-String to a std  string  A use case for me was having a pre-allocated char array  like C-String   but it s not NUL terminated   i e  SHA digest   The above syntax allows me to specify the length of the SHA digest of the char array so that std  string doesn t have to look for the terminating NUL char  which may or may not be there   Such as   unsigned char hashResult SHA DIGEST LENGTH       auto value   std  string reinterpret cast lt char  gt hashResult  SHA DIGEST LENGTH

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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

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You can cast CString freely to const char  and then assign it to an std  string like this    CString cstring  MyCString    std  string str    const char  cstring

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to convert CString to std  string  You can use this format   std  string sText CW2A CSText GetString    CP UTF8

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All other answers didn t quite address what I was looking for which was to convert CString on the fly as opposed to store the result in a variable    The solution is similar to above but we need one more step to instantiate a nameless object  I am illustrating with an example  Here is my function which needs std  string but I have CString   void CStringsPlayDlg  writeLog const std  string  amp text        std  string filename    c   test  test txt        std  ofstream log file filename c str    std  ios base  out   std  ios base  app        log file  lt  lt  text  lt  lt  std  endl      How to call it when you have a CString   std  string firstName    First   CString lastName    T  Last     writeLog  firstName          std  string  CT2A  lastName               Note that the last line is not a direct typecast but we are creating a nameless std  string object and supply the CString via its constructor

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All other answers didn t quite address what I was looking for which was to convert CString on the fly as opposed to store the result in a variable    The solution is similar to above but we need one more step to instantiate a nameless object  I am illustrating with an example  Here is my function which needs std  string but I have CString   void CStringsPlayDlg  writeLog const std  string  amp text        std  string filename    c   test  test txt        std  ofstream log file filename c str    std  ios base  out   std  ios base  app        log file  lt  lt  text  lt  lt  std  endl      How to call it when you have a CString   std  string firstName    First   CString lastName    T  Last     writeLog  firstName          std  string  CT2A  lastName               Note that the last line is not a direct typecast but we are creating a nameless std  string object and supply the CString via its constructor

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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

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You can use CT2CA   CString datasetPath  CT2CA st datasetPath   string dataset st

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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

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This works fine     Convert CString to std  string inline std  string to string const CString amp  cst        return CT2A cst GetString

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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

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Is there any problem    There are several issues    CString is a template specialization of CStringT  Depending on the BaseType describing the character type  there are two concrete specializations  CStringA  using char  and CStringW  using wchar t   While wchar t on Windows is ubiquitously used to store UTF-16 encoded code units  using char is ambiguous  The latter commonly stores ANSI encoded characters  but can also store ASCII  UTF-8  or even binary data  We don t know the character encoding  or even character type  of CString  which is controlled through the  UNICODE preprocessor symbol   making the question ambiguous  We also don t know the desired character encoding of std  string  Converting between Unicode and ANSI is inherently lossy  ANSI encoding can only represent a subset of the Unicode character set    To address these issues  I m going to assume that wchar t will store UTF-16 encoded code units  and char will hold UTF-8 octet sequences  That s the only reasonable choice you can make to ensure that source and destination strings retain the same information  without limiting the solution to a subset of the source or destination domains   The following implementations convert between CStringA CStringW and std  wstring std  string mapping from UTF-8 to UTF-16 and vice versa    include  lt string gt   include  lt atlconv h gt   std  string to utf8 CStringW const amp  src utf16        return   CW2A src utf16 GetString    CP UTF8  m psz       std  wstring to utf16 CStringA const amp  src utf8        return   CA2W src utf8 GetString    CP UTF8  m psz        The remaining two functions construct C   string objects from MFC strings  leaving the encoding unchanged  Note that while the previous functions cannot cope with embedded NUL characters  these functions are immune to that    include  lt string gt   include  lt atlconv h gt   std  string to std string CStringA const amp  src        return   src GetString    src GetString     src GetLength         std  wstring to std wstring CStringW const amp  src        return   src GetString    src GetString     src GetLength

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to convert CString to std  string  You can use this format   std  string sText CW2A CSText GetString    CP UTF8

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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  lt string gt   include  lt vector gt   include  lt cassert gt   include  lt exception gt    include  lt boost system system error hpp gt   include  lt boost integer traits hpp gt          Convert a Windows wide string to a UTF-8  multi-byte  string      std  string WideStringToUtf8String const std  wstring amp  wide        if  wide size    gt  boost  integer traits lt int gt   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 lt int gt  wide size              NULL  0  NULL  NULL           Perform actual conversion     if  len  gt  0                std  vector lt char gt  buffer len           len     WideCharToMultiByte              CP UTF8  0  wide c str    static cast lt int gt  wide size                  amp buffer 0   static cast lt int gt  buffer size     NULL  NULL           if  len  gt  0                        assert len    static cast lt int gt  buffer size                  return std  string  amp buffer 0   buffer size                          throw boost  system  system error            GetLastError    boost  system  system category

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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

User · Answer

Solve that by using std  basic string lt TCHAR gt  instead of std  string and it should work fine regardless of your character setting

User · Answer

One interesting approach is to cast CString to CStringA inside a string constructor  Unlike std  string s  LPCTSTR cs   this will work even if  UNICODE is defined  However  if that is the case  this will perform conversion from Unicode to ANSI  so it is unsafe for higher Unicode values beyond the ASCII character set  Such conversion is subject to the  CSTRING DISABLE NARROW WIDE CONVERSION preprocessor definition  https   msdn microsoft com en-us library 5bzxfsea aspx          CString s1  SomeString            string s2  CStringA s1

[c++] How do you convert CString and std::string std::wstring to each other?

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