Undefine reference for libraries, so How could I find the right path?

Undefine reference for libraries, so How could I find the right path?



I am trying to compile a v4l2 example in Ubuntu but I am getting the

following error:

guilherme@notedev01:~/Downloads/V4l2_samples-0.4.1$ make

gcc -O2 -L/usr/include -lX11 -lXext -o viewer viewer.c

/tmp/ccUjnjWQ.o: In function `image_destroy':

viewer.c:(.text+0x234): undefined reference to `XDestroyImage'

viewer.c:(.text+0x256): undefined reference to `XFreeGC'

viewer.c:(.text+0x277): undefined reference to `XShmDetach'

viewer.c:(.text+0x2ac): undefined reference to `XFreePixmap'

/tmp/ccUjnjWQ.o: In function `image_create':

viewer.c:(.text+0x305): undefined reference to `XCreateGC'

viewer.c:(.text+0x31d): undefined reference to `XGetWindowAttributes'

viewer.c:(.text+0x39e): undefined reference to `XShmCreateImage'

viewer.c:(.text+0x3f5): undefined reference to `XShmAttach'

viewer.c:(.text+0x44e): undefined reference to `XCreateImage'

viewer.c:(.text+0x494): undefined reference to `XShmQueryExtension'

viewer.c:(.text+0x4b4): undefined reference to `XShmPixmapFormat'

viewer.c:(.text+0x4dc): undefined reference to `XShmCreatePixmap'

/tmp/ccUjnjWQ.o: In function `image_put':

viewer.c:(.text+0x54c): undefined reference to `XPutImage'

viewer.c:(.text+0x586): undefined reference to `XShmPutImage'

/tmp/ccUjnjWQ.o: In function `main':

viewer.c:(.text.startup+0x18b): undefined reference to `XOpenDisplay'

viewer.c:(.text.startup+0x1b1): undefined reference to `XScreenOfDisplay'

viewer.c:(.text.startup+0x1ee): undefined reference to `XCreateSimpleWindow'

viewer.c:(.text.startup+0x249): undefined reference to `XMapRaised'

viewer.c:(.text.startup+0x263): undefined reference to `XStoreName'

viewer.c:(.text.startup+0x280): undefined reference to `XGetWindowAttributes'

viewer.c:(.text.startup+0x92f): undefined reference to `XPending'

viewer.c:(.text.startup+0x94c): undefined reference to `XNextEvent'

viewer.c:(.text.startup+0xaee): undefined reference to `XPending'

viewer.c:(.text.startup+0xb0b): undefined reference to `XNextEvent'

viewer.c:(.text.startup+0xf39): undefined reference to `XPending'

viewer.c:(.text.startup+0xf56): undefined reference to `XNextEvent'

collect2: error: ld returned 1 exit status

make: *** [viewer] Error 1

What I can see is that the path for -lx11 and -lXext isn't -L/usr/include.

How can I find the right path for those libraries?

Thanks.