How do I pass a LPCSTR to a c++ function convert to string and return a LPCSTR?

Question

I have a C++ API function that is called by Install Shield via InstallScript:

SQLHELPER_API LPCSTR GetAvailableAppName(LPCSTR appNameP)
{
    //return "this works just fine";
    std::string newAppName = "I work, maybe?";
    LPCSTR returnVal = newAppName.c_str();
    return returnVal;
}

The only thing that returns is an empty string. If I just return passed in variable "appNameP" it returns that just fine as well.

My main issue is that I need to pass in a LPCSTR and perform some string operation on it.

Answer 1

A LPCSTR is the same as const char *.

Passing a C-style string like that to a function call is fine.

Returning a pointer to a local function variable is not fine, because this local variable doesn´t exist anymore after the function ends. As soon as you´re using the pointer in main (or whereever the function was called), it points to a memory which doesn´t belong to you anymore, and the value may have changed already.

There are several possibilites, each with a downside:

1. Using only memory you got as parameter (eg. appNameP, because this has to be something from outside and will still exist after the function ends). Downside: You need to pass something fitting for that purpose => the function signature or at least the requirements for the parameters changes, and you´ve to check/change how it is called.

2. Allocating something with new. Downside: Somewhere later, outside, delete[] have to be called.

3. Returning something like std::string. Downside: As in #1, the function signature changes, and you´ve to change how it is called.

If InstallShield calls this function itself:

What InstallShield expects you to do should be somewhere in the documentation.