CODEWITHSUNDEEP
c++functionpointers
Astara
Astara

Reputation: 227

How to encapsulate returning ref to pointer to C_string?

I have some C++ code interfacing with 'X' code (as in X11). For one of the calls it wants to have a param be the address of a pointer to a string. The call is setup to take a counted array of strings. In this case, it's only taking 1 string (a winname derived from the hostname). What is currently in place is something along the lines of:

char winname_[257];    // to hold Cstr returned by gethostname()
string windowName{};   // holding string version (prefer strings, but need 
                       // Cstr's for C-compat in places)

Have functions:

string XWin::WindowName(string name) { 
  if (name.size()) windowName = name;
  if (!windowName.size()) {
    gethostname(winname_, sizeof(winname_)-1);
    windowName = getResourceOrUseDefault(string("title"), string(winname_));
    strcpy(winname_, windowName.c_str());
  }
  return windowName;
}

inline char * winname() {if (!winname[0]) WindowName();return winname;}

To pass to the Xfunc, I need:

char * winname_p = winname_;

As the X function takes:

Xfunc(&winname_p, 1, et, al.)

What I'd like to do is be able to encapsulate the "winname_p" reference in a function, so I can check that winname_p[0] != 0, and have the function return a pointer, but so far, I am flailing in having a function return an lvalue so I can have something like:

Xfunc(&winname_ptr(),1, et,al.)...

I haven't figured out the return syntax for the function so that it returns an lvalue to winname_p. I'm sure this is simple for many, but I seem to have some blocks when it comes to pointers & functions.

Upvotes: 0

Views: 69

Answers (1)

Astara
Astara

Reputation: 227

Like many things, this is easy once you know the answer. Initialize the pointer as a const (to indicate it shouldn't be changed):

char  * const winname_p{winname_};

Then the wrapper:

char * const &XWin::winname_ptr(void) {
    if (!winname_[0]) WindowName();
    return winname_p;
}

And the usage:

if (XStringListToTextProperty(
    const_cast<char **>(&winname_ptr()), 1, &title_) == 0) {...}

Would have been simpler to not use const, but it seems more accurate this way.

Upvotes: 1

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