gists/c-programming/io/freadln.c

/*
 * freadln.c
 *
 * The `freadln` function reads a line from STDIN into a string, allocating
 * memory for it.
 *
 * NOTE: Test: Declare macro NO_SIZE_T_FORMAT when compiling if your compiler
 * or glibc do not support `%zu` format specifier.
 * NOTE: Test: Declare macro POSIX when compiling if you're using a POSIX
 * system.
 *
 * 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
 *
 * Author: Intel A80486DX2-66
 * License: Creative Commons Zero 1.0 Universal
 */

#include "freadln.h"

int freadln(FILE* f, 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_EOF: end of file
	 * 	freadln_ERROR: an error occurred (see errno)
	 */

	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
	if (f == stdin)
		fflush(stdout);

	freadln_length_type length = 0; // initial length

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

	int character;
	while ((character = fgetc(f)) != EOF && character != EOT
	       /* 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_epilogue;
			return freadln_ERROR;
		} 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_epilogue;
			return freadln_ERROR;
		}

		*output = temp;
	}

	errno = 0;
	freadln_epilogue;
	if (character == EOF)
		return freadln_EOF;
	return freadln_OK;
}

#ifdef TEST
# include <ctype.h>
# include <inttypes.h>
# include <stdbool.h>
# include <stdint.h>

# if POSIX
#  include <unistd.h>
#  define SLEEP_FN sleep
#  define DO_SLEEP 1
# elif defined(_WIN32) || defined(WIN32)
#  include <windows.h>
#  define SLEEP_FN(x) Sleep((DWORD) (x))
#  define DO_SLEEP 1
# elif defined(__CYGWIN__) || defined(__unix__) || (defined(__APPLE__) && \
       defined(__MACH__)) || defined(__linux__) || defined(__FreeBSD__) || \
       defined(__NetBSD__) || defined(__OpenBSD__) || defined(__bsdi__) || \
       defined(__DragonFly__) || defined(__MINGW32__) || defined(__MINGW64__)
#  include <unistd.h>
#  define SLEEP_FN(x) usleep((x) * 1000ULL)
#  define DO_SLEEP 1
# else
#  define SLEEP_FN(...)
#  define DO_SLEEP 0
# endif
# if DO_SLEEP
#  include <time.h>
# endif

# ifndef NO_SIZE_T_FORMAT
#  if defined(__TINYC__) || (defined(__STDC_VERSION__) && \
      __STDC_VERSION__ < 199901L)
#   define NO_SIZE_T_FORMAT
#  endif
# endif

# if defined(NO_SIZE_T_FORMAT)
#  define PRIuSIZE PRIuMAX
typedef uintmax_t SIZE_T_FORMAT;
# else
#  define PRIuSIZE "zu"
typedef size_t SIZE_T_FORMAT;
# endif

# define YN(boolean) ((boolean) ? "yes" : "no")

bool file_exists(const char* path);

bool file_exists(const char* path) {
	FILE* f = fopen(path, "rb");
	return !((f == NULL
	       /* close file if it was successfully opened */ || (fclose(f), false))
	         && errno == ENOENT);
}

int main(void) {
	// stdin test
	printf("Type something> ");
	char* line;
	if (finreadln(&line, NULL) == freadln_ERROR) {
		perror("freadln");
		return EXIT_FAILURE;
	}
	printf("Input string: '%s' (%" PRIuSIZE " characters)\n", line,
	       (SIZE_T_FORMAT) strlen(line));

	// file test
#define TEST_FILE "freadln_test.txt"
	if (file_exists(TEST_FILE)) {
		fflush(stdout);
		fprintf(stderr, "Error: A file `" TEST_FILE "` exists. Are you sure "
		        "you want to continue and\noverwrite it? [[y = Enter]/n]: ");
		fflush(stderr);
		size_t line_length;
		if (finreadln(&line, &line_length) == freadln_ERROR) {
			perror("freadln");
			return EXIT_FAILURE;
		} else if (line_length >= 1) {
			if (tolower(line[0]) == 'n')
				return EXIT_FAILURE;
		}
	}

	FILE* f = fopen(TEST_FILE, "w");
	if (f == NULL) {
		perror("fopen");
		return EXIT_FAILURE;
	}
	fprintf(f, "Hello, world!\nAnother line\n\n");
	FILE* new_f = freopen(TEST_FILE, "r", f);
	if (new_f == NULL) {
		perror("freopen");
		return EXIT_FAILURE;
	}
	f = new_f;

	printf("Waiting for 4 seconds...\n");
	fflush(stdout);

	clock_t start;
	for (int i = 0; i < 4; i++) {
#if DO_SLEEP
		start = clock();
#endif

		size_t line_length;
		int result = freadln(f, &line, &line_length);
		if (result == freadln_ERROR) {
			perror("freadln");
			return EXIT_FAILURE;
		} else if (result == freadln_EOF || feof(f)) {
			printf("File: EOF, breaking the loop (returned by function? %s, "
			       "feof? %s)\n", YN(result == freadln_EOF), YN(feof(f)));
			break;
		}
		printf("File, line #%d: '%s' (%" PRIuSIZE " characters)\n", i + 1, line,
		       (SIZE_T_FORMAT) line_length);

		SLEEP_FN(1000 - ((long double) (clock() - start) * 1000.l) /
		         CLOCKS_PER_SEC);
	}
	fclose(f);

	remove(TEST_FILE);

	fflush(stdout);

	return 0;
}
#endif