Undefined reference to `initscr' Ncurses

Question

I'm trying to compile my project and I use the lib ncurse. And I've got some errors when compiler links files.

Here is my flags line in Makefile:

-W -Wall -Werror -Wextra -lncurses

I've included ncurses.h

Some layouts :

prompt$> dpkg -S curses.h
libslang2-dev:amd64: /usr/include/slcurses.h
libncurses5-dev: /usr/include/ncurses.h
libncurses5-dev: /usr/include/curses.h

prompt$> dpkg -L libncurses5-dev | grep .so
/usr/lib/x86_64-linux-gnu/libncurses.so
/usr/lib/x86_64-linux-gnu/libcurses.so
/usr/lib/x86_64-linux-gnu/libmenu.so
/usr/lib/x86_64-linux-gnu/libform.so
/usr/lib/x86_64-linux-gnu/libpanel.s

And here are my erros :

gcc -W -Wall -Werror -Wextra -I./Includes/. -lncurses -o Sources/NCurses/ncurses_init.o -c Sources/NCurses/ncurses_init.c
./Sources/NCurses/ncurses_init.o: In function `ncruses_destroy':
ncurses_init.c:(.text+0x5): undefined reference to `endwin'
./Sources/NCurses/ncurses_init.o: In function `ncurses_write_line':
ncurses_init.c:(.text+0xc5): undefined reference to `mvwprintw'
./Sources/NCurses/ncurses_init.o: In function `ncurses_init':
ncurses_init.c:(.text+0xee): undefined reference to `initscr'
collect2: error: ld returned 1 exit status

Thanks a lot

Answer 1

You need to change your makefile so that the -lncurses directive comes after your object code on the gcc command line, i.e. it needs to generate the command:

gcc -W -Wall -Werror -Wextra -I./Includes/. -o Sources/NCurses/ncurses_init.o -c Sources/NCurses/ncurses_init.c -lncurses

This is because object files and libraries are linked in order in a single pass.

Answer 2

In C++ , I fixed it just by linking the ncurses library .

Here is the command :

g++ main.cpp -lncurses

Answer 3

I got flags to correct order by using LDLIBS variable:

ifndef PKG_CONFIG
PKG_CONFIG=pkg-config
endif

CFLAGS+=-std=c99 -pedantic -Wall
LDLIBS=$(shell $(PKG_CONFIG) --libs ncurses)

Answer 4

man gcc | grep -A10 "\-l library"

-l library

Search the library named library when linking. (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.)

It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o -lz bar.o searches library z after file foo.o but before bar.o. If bar.o refers to functions in z, those functions may not be loaded.