How to use dialog.h in a c program

Question

I am trying to use dialog.hin my C program. For this I looked up the manual (man 3 dialog) and used the example code, which they have provided. This is how my C program look like (it is called main.c):

#include <dialog.h>

int main(void)
{
  int status;
  init_dialog(stdin, stdout);
  status = dialog_yesno(
    "Hello, in dialog-format",
    "Hello World!",
    0, 0);
  end_dialog();
  return status;
}

After research I figured out, that the dialog program is based on ncurses. So I have installed both libraries, which contains the required header files.

I am working on Debian so: apt install dialog libncurses5-dev libncursesw5-dev

In the next step I have called the compiler, and I have also linked the libraries: gcc main.c -ldialog -lncurses

But compiling did not succeed.

/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(util.o): In function `dlg_auto_size':
(.text+0x1a06): undefined reference to `sqrt'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(trace.o): In function `dlg_trace_win':
(.text+0x29c): undefined reference to `win_wch'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(trace.o): In function `dlg_trace_win':
(.text+0x2ab): undefined reference to `wunctrl'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(arrows.o): In function `dlg_draw_arrows2':
(.text+0x2c4): undefined reference to `_nc_wacs'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(arrows.o): In function `dlg_draw_arrows2':
(.text+0x2d6): undefined reference to `wadd_wch'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(arrows.o): In function `dlg_draw_arrows2':
(.text+0x43c): undefined reference to `_nc_wacs'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(arrows.o): In function `dlg_draw_arrows2':
(.text+0x44e): undefined reference to `wadd_wch'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(arrows.o): In function `dlg_draw_scrollbar':
(.text+0x878): undefined reference to `_nc_wacs'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(arrows.o): In function `dlg_draw_scrollbar':
(.text+0x88f): undefined reference to `wvline_set'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(inputstr.o): In function `dlg_index_columns':
(.text+0x932): undefined reference to `setcchar'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(inputstr.o): In function `dlg_index_columns':
(.text+0x93c): undefined reference to `wunctrl'
/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/libdialog.a(ui_getc.o): In function `dlg_getc':
(.text+0x603): undefined reference to `wget_wch'
collect2: error: ld returned 1 exit status

After research I found out that the missing references to some functions like win_wch, wunctrl, etc. are all defined in curses.h.

Regarding to this post (What's the difference between -lcurses and -lncurses when compiling C using ncurses lib?) ncurses and curses are the same due curses is linked to ncurses.

But anyway, I have tried to compile with the curses library too: gcc main.c -lcurses -lncurses -ldialog. But it did not work either.

What am I missing? Why did compiling fail?

Since libdialog is based on libncurses, try putting `-ldialog` *before* the other library lines. This used to be a thing, perhaps modern linkers don't have this issue, but worth a try. — Steve Friedl, May 23 '20 at 22:32

Steve Friedl · Accepted Answer · 2020-05-23T23:02:10.877

I did some testing on a Debian-based system (a Beaglebone), and this was not an obvious fix. Turns out there are multiple versions of the ncurses library, and the dialog library was built with one of them, just not the one you were using.

The way you're supposed to figure this out is with the dialog-config command, which has options to show which CFLAGS or libraries you need on the compile line (or in the makefile), but I didn't find it on my system, so I looked at /usr/include/dlg_config.h for some clues:

...
#define DLG_HAVE_LIBINTL_H 1
#define DLG_HAVE_LIBNCURSESW 1   <---
#define DLG_HAVE_LIMITS_H 1

Hmmm, this suggests it needs -lncursesw instead of -lncurses, so we see this compile:

$ gcc dlg.c -ldialog -lncursesw
/usr/bin/ld: /usr/lib/gcc/arm-linux-gnueabihf/8/../../../arm-linux-gnueabihf/libdialog.a(util.o): in function `dlg_auto_size':
(.text+0x13d2): undefined reference to `sqrt'

Ok, so a lot closer: sqrt() is in the math library, so adding -lm gets it over the goal line:

$ gcc dlg.c -ldialog -lncursesw -lm

It seems that ncursesw is a wide-character version that works with an international character set, which was new to me.

EDIT: Elaborating on the "dialog-config" stuff: The way you're supposed to do this is documented in the dialog(3) manual page:

gcc $(dialog-config --cflags) file ... $(dialog-config --libs)

The idea is that a package can publish what it needs to build in a command, so in this case I imagine that dialog-config --cflags might not output anything, but dialog-config --libs would output -ldialog -lncursesw -lm, so you could embed this in your makefile and have it do the right thing.

This paradigm is common, and on my system I see (for example) /usr/bin/python-config that shows how it was built on this machine:

$ python-config --cflags
-I/usr/include/python2.7 -I/usr/include/arm-linux-gnueabihf/python2.7
-fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g
-fdebug-prefix-map=/build/python2.7-RT6aMn/python2.7-2.7.16=.
-fstack-protector-strong -Wformat -Werror=format-security  -DNDEBUG
-g -fwrapv -O2 -Wall -Wstrict-prototypes

$ python-config --libs
-lpython2.7 -lpthread -ldl  -lutil -lm

If you were trying to build some kind of Python plugin, guessing the above parameters would be a real challenge.

Thanks, I would never have figured this out on my own. – csskevin May 23 '20 at 23:07 — csskevin, May 23 '20 at 23:07

How to use dialog.h in a c program

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