C readline function

Question

In an assignment for college it was suggested to use the C readline function in an exercise. I have searched for its reference but still haven't found it. Does it really exist? In which header? Can you please post the link to the reference?

Answer 1

Readline exists in two places, libreadline and libedit (also called libeditline). Both have an identical interface. The difference is libreadline is licensed under the GPL, libedit is 3 clause BSD. Licensing is really not a concern for an assignment, at least I don't think it is. Either license allows you to use the code freely. If you link against readline, be sure to make the whole program GPL 2 or later which will satisfy whatever version of the GPL governs the system readline. It may be GPL2+ or GPL3+, depending on the age of the system. I'm not advocating either license, that's up to you.

Note, take care to install either / or and adjust linking as needed (-lreadline or -ledit or -leditline). Both are libraries and not a part of the standard C library.

Edit (afterthought):

If releasing a program to the wild, its a nice gesture to allow the user to configure it with their readline of choice. For instance: --with-readline or --with-libedit, etc. This allows a binary package that conforms to their choice of license, at least as far as readline is concerned.

Links: Readline and Edit/Editline.

Answer 2

I don't think it's a standard function.

I simple implementation would be like this:

char *Readline(char *in) {
   char *cptr;

   if (cptr = fgets(in, MAX_LINE, stdin)) {
     /* kill preceding whitespace but leave \n so we're guaranteed to have something
     while(*cptr == ' ' || *cptr == '\t') {
       cptr++;
     }
     return cptr;    
    } else {
     return 0;
   }
 }

It uses fgets() to read up to MAX_LINE - 1 characters into the buffer 'in'. It strips preceding whitespace and returns a pointer to the first non-whitespace character.