gists/c-programming/io/freadln.c

/*
 * freadln.c
 *
 * The `freadln` function reads a line from STDIN into a string, allocating
 * memory for it.
 *
 * Author: Intel A80486DX2-66
 * License: Creative Commons Zero 1.0 Universal
 *
 * TODO: Figure out potential problems
 * TODO: Add 'flushing' of STDIN (while there are characters, read them) before
 * the input reading loop to avoid input queues
 * TODO: Add the feature of reading from arbitrary file, then extract a macro:
 * `#define finreadln(output, length_out) freadln(stdin, output, length_out)`
 */

#include "freadln.h"

ssize_t freadln(char** output, size_t* length_out) {
	/*
	 * The length of STDIN line is counted without any terminating characters.
	 *
	 * return value:
	 * 	freadln_OK: no errors, the length of STDIN line has been stored in
	 * 	`length_out`
	 * 	freadln_ERROR: an error occurred (see errno)
	 * 	>= 0: length of stdin line
	 */

	if (output == NULL)
		return freadln_ERROR;

	// NOTE: if the file is STDIN, flush STDOUT before waiting for input to
	// make sure a prompt is displayed
	fflush(stdout);

	freadln_length_type length = 0;

	*output = malloc((length + 1) * sizeof(char));
	if (*output == NULL)
		return freadln_ERROR;

	int character;
	while ((character = fgetc(stdin)) != EOF
	       /* stop on a newline character: */ && character != '\n') {
		(*output)[length] = (char) character;

		// integer overflow and integer limit check, to keep array boundaries
		if ((freadln_length_type) (length + 2) <= (freadln_length_type) length)
		{
			errno = ERANGE;
			freadln_success_epilogue;
		} else
			length++;

		char* temp = realloc(*output, (length + 1) * sizeof(char));

		// If the function fails to allocate new memory, return the string that
		// has already been accumulated.
		if (temp == NULL) {
			// keep errno;
			freadln_success_epilogue;
		}

		*output = temp;
	}

	errno = 0;
	freadln_success_epilogue;
}