readline AWOL?

[Roger Oberholtzer]

On Nov 18, 2008, at 2:05 PM, Dog Walker wrote:

> On Mon, Nov 17, 2008 at 12:40 PM, Jorge Almeida  
> <jjalmeida at gmail.com> wrote:
>> Hello, C-wise people,
>>
>> Can someone understand this?
>>
>>       $ cat readtest.c
>>       #include <stdio.h>
>>       #include <readline/history.h>
>>       #include <readline/readline.h>
>>       #define MAINPROMPT ">"
>>       int main(int argc, char *argv[])
>>       {
>>                       char *lp;
>>                       lp=readline(MAINPROMPT);
>>                       return 0;
>>       }
>>       $ gcc readtest.c
>>       /tmp/cc88uLvp.o: In function `main':
>>       readtest.c:(.text+0x19): undefined reference to `readline'
>>       collect2: ld returned 1 exit status
>>       $ ls /usr/include/readline
>>       chardefs.h  history.h  keymaps.h  readline.h  rlconf.h   
>> rlstdc.h
>> rltypedefs.h  tilde.h
>>
>> Tested in Gentoo and in FC5.
>>
>>> From man 3 readline:
>>
>>       SYNOPSIS
>>              #include <stdio.h>
>>              #include <readline/readline.h>
>>              #include <readline/history.h>
>>
>>              char *
>>              readline (const char *prompt);
>>
>>
>
> I would try doing what it says, i.e., declaring the readline function
> before you use it:
>
>        char *
>        readline (const char *prompt);
>        int main(int argc, char *argv[])
>        {
>                      char *lp;
>                      lp=readline(MAINPROMPT);
>                      return 0;
>        }
>

This is not what the error is complaining about. It is complaining  
about something in a .o file. gcc will happily make a .o file without  
a function prototype. But it will not make an executable without all  
references being satisfied. And that is what is happening here. It is  
very very very (times a big number) bad form to declare function  
prototypes on your own that mask those in files you include. Unless  
there is damned good reason. And it should be surrounded by #error  
messages so you are reminded each time you compile that this is done.
>

Roger Oberholtzer

OPQ Systems / Ramböll RST

Ramböll Sverige AB
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And remember:

It is RSofT and there is always something under construction.
It is like talking about large city with all constructions finished.
Not impossible, but very unlikely.