When i compile acode i have this error cannot open file X11/Xlib.h in c++ - c++

Question

/* Sequential Mandelbrot program mandelbrot.c */
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/Xos.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#define X_RESN 800 /* x resolution */
#define Y_RESN 800 /* y resolution */
typedef struct complextype
{ float real, imag;
} Compl;
int main (int argc, char *argv[])
{ Window win; /* window initialization */
unsigned
int width, height, /* window size */
x, y, /* window position */
border_width, /* border width in pixels */
display_width,
display_height, /* size of screen */
screen; /* which screen */
char *window_name = "Mandelbrot Set", *display_name = NULL;
GC gc;
unsigned long valuemask = 0;
XGCValues values;
Display *display;
XSizeHints size_hints;
Pixmap bitmap;
XPoint points[800];
FILE *fp, *fopen ();
char str[100];
XSetWindowAttributes attr[1];
/* Mandlebrot variables */
int i, j, k;
Compl z, c;
float lengthsq, temp;
/* connect to Xserver */
if ( (display = XOpenDisplay (display_name)) == NULL )
{ fprintf (stderr, "drawon: cannot connect to X server %s\n",
XDisplayName (display_name) );
exit (-1);
}
/* get screen size */
screen = DefaultScreen (display);
display_width = DisplayWidth (display, screen);
display_height = DisplayHeight (display, screen);
/* set window size */
width = X_RESN;
height = Y_RESN;
/* set window position */
x = 0;
y = 0;
/* create opaque window */
border_width = 4;
win = XCreateSimpleWindow(display, RootWindow (display, screen),
x, y, width, height, border_width,
BlackPixel (display, screen), WhitePixel (display, screen));
size_hints.flags = USPosition|USSize;
size_hints.x = x;
size_hints.y = y;
size_hints.width = width;
size_hints.height = height;
size_hints.min_width = 300;
size_hints.min_height = 300;
XSetNormalHints (display, win, &size_hints);
XStoreName(display, win, window_name);
/* create graphics context */
gc = XCreateGC (display, win, valuemask, &values);
XSetBackground (display, gc, WhitePixel (display, screen));
XSetForeground (display, gc, BlackPixel (display, screen));
XSetLineAttributes (display,gc,1,LineSolid,CapRound,JoinRound);
attr[0].backing_store = Always;
attr[0].backing_planes = 1;
attr[0].backing_pixel = BlackPixel(display, screen);
XChangeWindowAttributes(display, win,
CWBackingStore | CWBackingPlanes | CWBackingPixel, attr);
XMapWindow (display, win);
XSync(display, 0);
/* Calculate and draw points */
for(i=0; i < X_RESN; i++)
{ for(j=0; j < Y_RESN; j++)
{ z.real = z.imag = 0.0; /* 800x800 scale factors */
c.real = ((float) j - 400.0)/200.0;
c.imag = ((float) i - 400.0)/200.0;
k = 0;
do
{ /* iterate for pixel color */
temp = z.real*z.real - z.imag*z.imag + c.real;
z.imag = 2.0*z.real*z.imag + c.imag;
z.real = temp;
lengthsq = z.real*z.real+z.imag*z.imag;
k++;
} while (lengthsq < 4.0 && k < 100);
if (k == 100) XDrawPoint (display, win, gc, j, i);
} }
XFlush (display);
sleep (30);
/* Program Finished */
}

Answer 1

Open up a command prompt and run the two commands:
find / -type f - name Xlib.h
find / -type d - name X11
That should help you locate that file and/or directory so you can see whether it's available.
If it is available (e.g., it's found at /usr/include/X_stuff/X11/Xlib.h), make sure your compiler command references it, like:
g++ -I/usr/include/X_stuff ...
If it's not there, install it.

Answer 2

Either you forgot to install the X development packages, or the directory containing the headers was not added to the includedir list.