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?
5 Answers
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.
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.
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:
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);
}
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.
