将std :: string转换为const tchar *

Question

I have a function that takes in a parameter called arrayOfStrings defined as below:

const TCHAR* arrayOfStrings[] = { L"Test" };

Now I would like to convert strings to the type above, but I don't know how. This link provides a solution for converting string to tchar, but not const tchar*. This other link shows how to convert string to tchar*, but not const tchar*, and the memory allocation is a problem for me with this second solution. As you can probably tell, I am very new to c++, so any educational tips would be appreciated as well.

Answer 1

A simple approach, which will work with all C++ standards, would be

 #include <string>

 #include <windows.h>    //   or whatever header you're using that specifies TCHAR

 int main()
 {
       std::string test("Hello");     //   string to be converted

       //   first, if you need a const TCHAR *

       std::basic_string<TCHAR> converted(test.begin(), test.end());

       const TCHAR *tchar = converted.c_str();

       //   use tchar as it is in the required form (const)

       //   second, if you need a TCHAR * (not const)

       std::vector<TCHAR> converted2(test.begin(), test.end());

       TCHAR *tchar2 = &converted2[0];

       // use tchar2 as it is of the required form (non-const).

 }

std::basic_string does not provide a means in all C++ standards to obtain a non- const pointer to its data, but std::vector does. (Assuming you don't use an explicit conversion to introduce or remove const ness).

In C++17 and later, things are simpler: the basic_string::data() has both a const and non- const overload, which wasn't the case before the 2017 standard. Before C++11, the data in a basic_string was not guaranteed to be contiguous by the standard (even if implementations typically implemented things that way) but c_str() did provide the address of the first character of a contiguous array. The net effect is that, in C++17 and later, appropriate overloads of basic_string::data() or basic_string::c_str() can be used, without a need for cast to change const ness, and without resorting to a vector (which has been guaranteed to have contiguous elements in all C++ standards).

Points to note in both cases

1. The pointers ( tchar and tchar2 ) are invalidated if their respective containers ( converted or converted2 ) are resized or if they cease to exist. For example, don't use the data pointed to by tchar if converted has passed out of scope, since data tchar points at will no longer exist.
2. It is simply undefined behaviour to use the pointers to run past the end (no magical resizing when using the pointers).