How to convert std string to LPCSTR

Question

How can I convert a std  string to LPCSTR  Also  how can I convert a std  string to LPWSTR   I am totally confused with these LPCSTR LPSTR LPWSTR and LPCWSTR   Are LPWSTR and LPCWSTR the same

User · Answer

These are Microsoft defined typedefs which correspond to:

LPCSTR: pointer to null terminated const string of char

LPSTR: pointer to null terminated char string of char (often a buffer is passed and used as an 'output' param)

LPCWSTR: pointer to null terminated string of const wchar_t

LPWSTR: pointer to null terminated string of wchar_t (often a buffer is passed and used as an 'output' param)

To "convert" a std::string to a LPCSTR depends on the exact context but usually calling .c_str() is sufficient.

This works.

void TakesString(LPCSTR param);

void f(const std::string& param)
{
    TakesString(param.c_str());
}

Note that you shouldn't attempt to do something like this.

LPCSTR GetString()
{
    std::string tmp("temporary");
    return tmp.c_str();
}

The buffer returned by .c_str() is owned by the std::string instance and will only be valid until the string is next modified or destroyed.

To convert a std::string to a LPWSTR is more complicated. Wanting an LPWSTR implies that you need a modifiable buffer and you also need to be sure that you understand what character encoding the std::string is using. If the std::string contains a string using the system default encoding (assuming windows, here), then you can find the length of the required wide character buffer and perform the transcoding using MultiByteToWideChar (a Win32 API function).

e.g.

void f(const std:string& instr)
{
    // Assumes std::string is encoded in the current Windows ANSI codepage
    int bufferlen = ::MultiByteToWideChar(CP_ACP, 0, instr.c_str(), instr.size(), NULL, 0);

    if (bufferlen == 0)
    {
        // Something went wrong. Perhaps, check GetLastError() and log.
        return;
    }

    // Allocate new LPWSTR - must deallocate it later
    LPWSTR widestr = new WCHAR[bufferlen + 1];

    ::MultiByteToWideChar(CP_ACP, 0, instr.c_str(), instr.size(), widestr, bufferlen);

    // Ensure wide string is null terminated
    widestr[bufferlen] = 0;

    // Do something with widestr

    delete[] widestr;
}

User · Answer

Converting is simple   std  string myString   LPCSTR lpMyString   myString c str      One thing to be careful of here is that c str does not return a copy of myString  but just a pointer to the character string that std  string wraps  If you want need a copy you ll need to make one yourself using strcpy

User · Answer

std  string myString  SomeValue    LPSTR lpSTR   const cast lt char  gt  myString c str       myString is the input string and lpSTR is it s LPSTR equivalent

User · Answer

str c str   gives you a const char    which is an LPCSTR  Long Pointer to Constant STRing  -- means that it s a pointer to a 0 terminated string of characters   W means wide string  composed of wchar t instead of char

User · Answer

The MultiByteToWideChar answer that Charles Bailey gave is the correct one  Because LPCWSTR is just a typedef for const WCHAR   widestr in the example code there can be used wherever a LPWSTR is expected or where a LPCWSTR is expected   One minor tweak would be to use std  vector lt WCHAR gt  instead of a manually managed array      using vector  buffer is deallocated when function ends std  vector lt WCHAR gt  widestr bufferlen   1      MultiByteToWideChar CP ACP  0  instr c str    instr size     amp widestr 0   bufferlen       Ensure wide string is null terminated widestr bufferlen    0      no need to delete  handled by vector   Also  if you need to work with wide strings to start with  you can use std  wstring instead of std  string  If you want to work with the Windows TCHAR type  you can use std  basic string lt TCHAR gt   Converting from std  wstring to LPCWSTR or from std  basic string lt TCHAR gt  to LPCTSTR is just a matter of calling c str  It s when you re changing between ANSI and UTF-16 characters that MultiByteToWideChar  and its inverse WideCharToMultiByte  comes into the picture

User · Answer

The conversion is simple   std  string str  LPCSTR lpcstr   str c str

User · Answer

Call c str   to get a const char    LPCSTR  from a std  string   It s all in the name   LPSTR -  long  pointer to string - char    LPCSTR -  long  pointer to constant string - const char    LPWSTR -  long  pointer to Unicode  wide  string - wchar t    LPCWSTR -  long  pointer to constant Unicode  wide  string - const wchar t    LPTSTR -  long  pointer to TCHAR  Unicode if UNICODE is defined  ANSI if not  string - TCHAR    LPCTSTR -  long  pointer to constant TCHAR string - const TCHAR    You can ignore the L  long  part of the names -- it s a holdover from 16-bit Windows

User · Answer

Using LPWSTR you could change contents of string where it points to  Using LPCWSTR you couldn t change contents of string where it points to   std  string s   SOME STRING     get temporary LPSTR  not really safe  LPSTR pst    s 0      get temporary LPCSTR  pretty safe  LPCSTR pcstr   s c str       convert to std  wstring std  wstring ws   ws assign  s begin    s end         get temporary LPWSTR  not really safe  LPWSTR pwst    ws 0      get temporary LPCWSTR  pretty safe  LPCWSTR pcwstr   ws c str      LPWSTR is just a pointer to original string  You shouldn t return it from function using the sample above  To get not temporary LPWSTR you should made a copy of original string on the heap  Check the sample below   LPWSTR ConvertToLPWSTR  const std  string  s       LPWSTR ws   new wchar t s size   1       1 for zero at the end   copy  s begin    s end    ws      ws s size      0     zero at the end   return ws     void f       std  string s   SOME STRING    LPWSTR ws   ConvertToLPWSTR  s          some actions    delete   ws     caller responsible for deletion

User · Answer

The easiest way to convert a std  string to a LPWSTR is in my opinion    Convert the std  string to a std  vector lt wchar t gt  Take the address of the first wchar t in the vector    std  vector lt wchar t gt  has a templated ctor which will take two iterators  such as the std  string begin   and  end   iterators  This will convert each char to a wchar t  though  That s only valid if the std  string contains ASCII or Latin-1  due to the way Unicode values resemble Latin-1 values  If it contains CP1252 or characters from any other encoding  it s more complicated  You ll then need to convert the characters

[c++] How to convert std::string to LPCSTR?

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