cannot convert from 'std::string' to 'LPSTR'

Question

As I clould not pass LPCSTR from one function to another (Data get changed) I tried passing it as a string.

But later I need to again convert it back to LPSTR. While trying the conversion I am getting the above error:

cannot convert from 'std::string' to 'LPSTR'

How can I resolve this?

Answer 1

Are you running somestringvariablename.c_str()? That should work.

Answer 2

There is a function on std::string c_str() . However I doubt that you could not use a std::string in your case.

Answer 3

An LPSTR can be substituted with by using a TCHAR (i.e. found in tchar.h). So if you have a std::string, you can use the method std::string::c_str().

Answer 4

If the function, you are calling does not write to string, but only reads it, then you can simply use string::c_str method. If it is going to write something, then you probably should ensure that your string has enough space by calling string::reserve().

Answer 5

That's just because you should use std::string::c_str() method.

But this involves const_cast in given case because const char * returned by c_str() can not be assigned to a non-constant LPSTR.

std::string str = "something";
LPSTR s = const_cast<char *>(str.c_str());

But you must be sure that lifetime of str will be longer that that of LPTSTR variable.

Another mention, if code compiles as Unicode-conformant, then types LPTSTR and std::string are incompatible. You should use std::wstring instead.

Answer 6

If you need an LPSTR, that means the string will/may be modified. std::string::c_str() returns a const pointer, and you can't just const_cast it away and hope all is good in the world, because it isn't. The string may be changed in all sorts of nasty ways, and your original std::string will be oblivious to all of them.

Try this instead:

// myFunction takes an LPSTR
std::string cppString = "something";
LPSTR cString = strdup( cppString.c_str() );
try {
   myFunction( cString );
   cppString = cString;
} catch(...) {
   free( cString );
}

Wrap the string in a smart pointer and get rid of the try...catch for bonus points (don't forget the custom deleter).