undefined reference to `readline' [duplicate]

Question

I'm having a problem trying to run the GNU Readline library sample code available in wikipedia. Here it goes:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <readline/readline.h>
#include <readline/history.h>

int main()
{
    char* input, shell_prompt[100];

    // Configure readline to auto-complete paths when the tab key is hit.
    rl_bind_key('\t', rl_complete);

    for(;;) {
        // Create prompt string from user name and current working directory.
        snprintf(shell_prompt, sizeof(shell_prompt), "%s:%s $ ", getenv("USER"), getcwd(NULL, 1024));

        // Display prompt and read input (n.b. input must be freed after use)...
        input = readline(shell_prompt);

        // Check for EOF.
        if (!input)
            break;

        // Add input to history.
        add_history(input);

        // Do stuff...

        // Free input.
        free(input);
    }
}

I'm working on a restricted environment were readline was not available, so I had to download the sources, compile it and install it to my home dir.

This is the structure inside my home directory:

.local
├── include
│   └── readline
│       ├── chardefs.h
│       ├── history.h
│       ├── keymaps.h
│       ├── readline.h
│       ├── rlconf.h
│       ├── rlstdc.h
│       ├── rltypedefs.h
│       └── tilde.h
└── lib
    ├── libhistory.a
    ├── libhistory.so -> libhistory.so.6
    ├── libhistory.so.6 -> libhistory.so.6.2
    ├── libhistory.so.6.2
    ├── libreadline.a
    ├── libreadline.so -> libreadline.so.6
    ├── libreadline.so.6 -> libreadline.so.6.2
    └── libreadline.so.6.2

The problem is, when I call gcc it throws me an error:

$ gcc hello.c -o hello_c.o -I /home/my-home-dir/.local/include
/tmp/cckC236E.o: In function `main':
hello.c:(.text+0xa): undefined reference to `rl_complete'
hello.c:(.text+0x14): undefined reference to `rl_bind_key'
hello.c:(.text+0x60): undefined reference to `readline'
hello.c:(.text+0x77): undefined reference to `add_history'
collect2: error: ld returned 1 exit status

There is an answer about this here, but I'm not using Netbeans and I'm not quite sure how to specify the path to the library on the command line.

I tried to tell the linker where the libraries are, but the result is still the same:

$ gcc hello.c -o hello_c.o -I /home/my-home-dir/.local/include -Xlinker "-L /home/my-home-dir/.local/lib"
/tmp/cceiePMr.o: In function `main':
hello.c:(.text+0xa): undefined reference to `rl_complete'
hello.c:(.text+0x14): undefined reference to `rl_bind_key'
hello.c:(.text+0x60): undefined reference to `readline'
hello.c:(.text+0x77): undefined reference to `add_history'
collect2: error: ld returned 1 exit status

Any ideas what I might be missing here?

Answer 1

You need to link against the actual library using -lreadline in gcc arguments.