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Xlib, XFetchName compile error

Error:
olib.cpp: In function `void query(int)':
olib.cpp:70: error: cannot convert `char* (*)[256]' to `char**' for argument `3
' to `int XFetchName(Display*, long unsigned int, char**)'

This is the offending code method:

void query(int w)
{
Display *d = XOpenDisplay(0);
Window null, *wlist;
unsigned int n;
XQueryTree(d, DefaultRootWindow(d), &null, &null, &wlist, &n);
XFlush(d);
for (int i = 0; i<n; i++)
{
if(viewable(wlist[i]) == 1)
{
char *windowname[256];
XFetchName(d, wlist[i], &windowname); // This is the particular line causing the error.
cout << windowname << "\n";
if (windowname) XFree(windowname);
}
}
}

I guess the crux of my problem is that I don't know what the difference between a char * (*) and a char ** is?

Thanks in advance for any suggestions.

NovaDenizen

I think you just need to change the line to:
XFetchName(d, wlist[i], windowname);

The ampersand is unnecessary. char *windowname[256], an array of char *'s, looks like 'char **'. &windowname doesn't make much sense, since it is basically like taking the address of a literal constant. Since windowname is an array, it is its own pointer to itself.

ASKER CERTIFIED SOLUTION

jkr

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NovaDenizen

You're right, jkr. I didn't check the API, I just wanted to get rid of the syntax error.

jkr

>>I didn't check the API, I just wanted to get rid of the syntax error

That would work 'syntax-wise', but IMHO then 'XFree(windowname);' would lead to an error. It's the ole "who allocates it, frees it" rule that can lead to so much confusion is complex systems with a lot of DLLs and other libraries involved...

cs02rm0

ASKER

Thanks. Spot on :)