CODEWITHSUNDEEP
creadline
nunos
nunos

Reputation: 21409

Where is the readline function located in C?

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?

Upvotes: 18

Views: 95112

Answers (5)

Pavel Radzivilovsky
Pavel Radzivilovsky

Reputation: 19104

It doesn't exist.

They were mistaken and referred to gets() from stdio.h.

Also this is a very unsafe function due to no maximum size to read parameter, making it immediate security whole (lookup buffer overrun attack). You may use fgets() instead.

Upvotes: -6

Ajay Sharma
Ajay Sharma

Reputation: 31

Not sure if you tried reading this from the GNU C Library: ssize_t getline (char **lineptr, size_t *n, FILE *stream). This function reads a line from a file and can even re-allocate more space if needed.

An example of this is found in the manpage of getline. Below is a copy of it.

   #define _GNU_SOURCE
   #include <stdio.h>
   #include <stdlib.h>

   int
   main(int argc, char *argv[])
   {
       FILE *stream;
       char *line = NULL;
       size_t len = 0;
       ssize_t nread;

       if (argc != 2) {
           fprintf(stderr, "Usage: %s <file>\n", argv[0]);
           exit(EXIT_FAILURE);
       }

       stream = fopen(argv[1], "r");
       if (stream == NULL) {
           perror("fopen");
           exit(EXIT_FAILURE);
       }

       while ((nread = getline(&line, &len, stream)) != -1) {
           printf("Retrieved line of length %zu:\n", nread);
           fwrite(line, nread, 1, stdout);
       }

       free(line);
       fclose(stream);
       exit(EXIT_SUCCESS);
   }

Upvotes: 3

iGeeks
iGeeks

Reputation: 192

If you need a "readLine()" function, like the readLine() in Java-BufferedReader, you can also freely use my function «char* get_line(FILE *filePointer)» in "line.h", which I wrote just for this purpose: https://github.com/pheek/line.h/blob/master/line.h

Upvotes: 0

user50049
user50049

Reputation:

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.

Upvotes: 22

yassin
yassin

Reputation: 6707

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.

Upvotes: 3

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