ncurses doesn't work with -lncurses

Question

I try to use ncurses library in Ubuntu 12.04 LTS. It doesn't work. I go to step by step:

1. Install:

   
   sudo apt-get update
   sudo apt-get install libncurses-dev
   

2. main.cpp:

   #include <curses.h>
   #include <ncurses.h>
   int main(int argc, char *argv[])
   {
       initscr();      // Start curses mode
       printw("Hello World !!!");
       refresh();      // Print it on to the real screen
       getch();        // Wait for user input
       endwin();       // End curses mode
   }
   

3. makefile, add -lncurses to link and compile:

   
   all: main
   OBJS = main.o
   CXXFLAGS  += -std=c++0x
   CXXFLAGS  += -c -Wall
   main: $(OBJS)
       g++ -lncurses $^ -o $@
   %.o: %.cpp %.h
       g++ $(CXXFLAGS) -lncurses $<
   main.o: main.cpp
   clean:
       rm -rf *.o *.d main
       reset
   run:
       ./main
   

4. build (get error):

   $ make
   g++ -std=c++0x -c -Wall   -c -o main.o main.cpp
   g++ -lncurses main.o -o main
   main.o: In function `main':
   main.cpp:(.text+0xa): undefined reference to `initscr'
   main.cpp:(.text+0x16): undefined reference to `printw'
   main.cpp:(.text+0x1b): undefined reference to `refresh'
   main.cpp:(.text+0x20): undefined reference to `stdscr'
   main.cpp:(.text+0x28): undefined reference to `wgetch'
   main.cpp:(.text+0x2d): undefined reference to `endwin'
   collect2: ld returned 1 exit status
   make: *** [main] Error 1
   

Did I miss something?

Answer 1

The linker processes arguments in the order they're specified, keeping track of unresolved symbols in earlier arguments and resolving them as they're found in later arguments. Which means that the -lncurses argument (which defines the symbols) has to follow the main.o argument (which refers to them).

In your Makefile, change this:

main: $(OBJS)
    g++ -lncurses $^ -o $@

to this:

main: $(OBJS)
    g++ $^ -lncurses -o $@