LPCTSTR to const char*

Question

LPCTSTR to const char*

Flaviu_ 1,031

In a MFC project, I have encoutnered an issue using CDatabase::ExecuteSQL method, whend I have tried to deliver a std::string as a parameter:

void ExecuteSQL(LPCTSTR lpszSQL);

std::string sql;
ExecuteSQL(sql.c_str());

in Use Unicode Character Set configuration only.

The error is:

'void CDatabase::ExecuteSQL(LPCTSTR)': cannot convert argument 1 from 'const _Elem *' to 'LPCTSTR'

note: Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

So, which one of conversion is better ? reinterpret_cast or C-style cast ? Or doesn't matter ?

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Answer 1

RLWA32 49,636

A cast won't solve the problem. The std::string is encapsulating a narrow string. So the member function c_str() is returning a const char * pointer. You need to convert the result to UNICODE or otherwise change the code to use std::wstring when building for UNICODE.

Flaviu_ 1,031 Reputation points

2021-06-20T08:28:38.833+00:00

But how can do in order to be OK with Use Unicode Character Set and Use Multi-Byte Character Set without using stringstream ?

RLWA32 49,636

One way is old-fashioned conditional compilation -

        //  Example 1
        #ifdef UNICODE
            std::wstring sql;
        #else
            std::string sql;
        #endif

Another way is to use a typedef -

        //  Example 2
        typedef std::basic_string<TCHAR> tstring;

        tstring sql;

Flaviu_ 1,031 Reputation points

2021-06-20T09:41:03.343+00:00

Unfortunately, I don't think I can use any of them, the code should be compatible with old compilers. If not, I could use std::stringstream or std::basic_stringstream or something.
RLWA32 49,636 Reputation points

2021-06-20T10:24:24.163+00:00

How are the examples not compatible?
Igor Tandetnik 1,116 Reputation points

2021-06-20T13:19:48.907+00:00

How old is "old"? These techniques worked just fine in VC6, a 23-year old compiler.
RLWA32 49,636 Reputation points

2021-06-20T13:43:21.32+00:00

Thanks, I got a good laugh from this observation.
Flaviu_ 1,031 Reputation points

2021-06-20T18:31:35.253+00:00
I have used this approach and works.

#ifdef UNICODE std::wstring sql; #else std::string sql; #endif

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LPCTSTR to const char*

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