Ubuntu readline() and makefiles - c

Question

I have really simple program that checks if the word that user types is palindrome: ( I know that this program could be written much better but let's leave that aside for now )
I have to use readline function to get users input or create my own, but because I don't have enough knowledge to create my own I'm using readline.
#include <stdio.h>
#include <stdlib.h>
#include <readline/readline.h>
#include <readline/history.h>
int IsPalindrome(char* niz)
{
int y=0;
int n=0;
int i;
for(i=1;i<strlen(niz)/2+1;i++)
{
if(niz[i-1]==niz[strlen(niz)-i]){
y++;
}
else{
n++;
}
}
if(n>0){
return 0;
}
else{
return 1;
}
}
int main()
{
char *inpt;
inpt = readline("enter text: ");
if(IsPalindrome(inpt)==1)
{
printf("\nIs palindrome\n");
}
else{
printf("\nNot palindrome\n");
}
return 0;
}
I'm using Code::Blocks and if I click on "build and run" I get following error:
Undefined reference to 'readline'
I have to compile and then run my program from terminal with makefile and this is where I'm lost. I just recently started using Ubuntu so I don't really know much about it and how it works.
Now I have to compile my program with makefile ( all in run ). This is makefile that we can use ( I'm at university and we got this as help ) we just have to change some data ( name of the program, add some flags ):
GCC=gcc
CFLAGS=-c -g
LFLAGS=-lreadline
EXE=main
all: ${EXE}.o
${GCC} ${LFLAGS} ${EXE}.o -o ${EXE}
${EXE}.o: ${EXE}.c
${GCC} ${CFLAGS} ${EXE}.c
clean:
rm -rf *.o
rm -rf ${EXE}
Now because I'm using readline function I added flag -lreadline and added name of my program to EXE=main ( my program is called main.c ) but if I run makefile ( make all ) I get following error:
make all
gcc -lreadline main.o -o main
main.o: In function `main':
/home/yack/Desktop/NPO/Palindrom/Palindrom/main.c:67: undefined reference to `readline'
collect2: error: ld returned 1 exit status
Makefile:7: recipe for target 'all' failed
make: *** [all] Error 1
I installed Readline-6.3 and I was reading on the internet that I have to somehow link readline to tell compiler about it or something but looks like adding -lreadline flag is not enough.
Yesterday I found temporary fix so that I could test if my program works with this command:
gcc main.c -L/usr/local/lib -I/usr/local/include -lreadline -c -g
With this command I managed to create executable file and test if my program works, but today even that doesn't work anymore.
NOTE:
I have to compile my program from makefile, the last command in terminal was just to check if my program works since my makefile didn't work.
What am I doing wrong ?

Answer 1

The order of arguments passed to GCC (and the linker) is relevant.
Your Makefile should have the use of libreadline come before where you actually link libreadline with LFLAGS, like so:
GCC=gcc
CFLAGS=-c -g
LFLAGS=-lreadline
EXE=main
all: ${EXE}.o
${GCC} ${EXE}.o -o ${EXE} ${LFLAGS}
${EXE}.o: ${EXE}.c
${GCC} ${CFLAGS} ${EXE}.c
clean:
rm -rf *.o
rm -rf ${EXE}
In your "temporary fix" you fixed the ordering, and that is why it worked for you.