error C2440: 'initializing' : cannot convert from

Question

While using SQLite in C++98, how to convert stringstream to Unicode and pass it to sqlite3_exec()? I constantly have this error:

error C2440: 'initializing' : cannot convert from 'std::basic_string<_Elem,_Traits,_Ax>' to 'std::basic_string<_Elem,_Traits,_Ax>'
1>        with"

Code:

int main(int argc, char* argv[]) {
    sqlite3 *db;
    char *zErrMsg = 0;
    int rc;
    char *sql;
    const char* data = "Callback function called";
    tstringstream tstrsSQL;
    tstrsSQL.imbue(std::locale("C"));

    std::string s = tstrsSQL.str(); // converting stringstream to char?
    const char* p = s.c_str();

    /* Open database */
    rc = sqlite3_open("db.db3", &db);

    if( rc ) {
        fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
        return(0);
    } else {
        fprintf(stderr, "Opened database successfully\n");
    }

    /* Create SQL statement */
    tstrsSQL << _T("SELECT") something ("FROM") << table;

    /* Execute SQL statement */
    rc = sqlite3_exec(db, p, callback, (void*)data, &zErrMsg); // p needs to be unicode

Answer 1

You are using tstringstream, which I guess uses std::wstringstream if UNICODE is defined, so its str() gives a std::basic_string<wchar_t>.

But you get the result into a std::string, which is std::basic_string<char>. So the assignment fails.

Anyway, you take the result and use it in sqlite3_exec(), which takes a const char* as input.

That's why you shouldn't use tstringstream, you should use std::stringstream, and remove the _T from all of the string literals.

Minimal, complete, working code:

#include <iostream>
#include <sstream>
using namespace std;

int main()
{
    stringstream strstream;
    strstream << "Hello World";
    string str = strstream.str();
    cout << str << endl;
    return 0;
}