freadln.*: implement reading lines from arbitrary file

c-programming/io/freadln.c

@@ -10,13 +10,12 @@
  * 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)`
+ * FIXME: Handle EOF in a special way to indicate EOF
  */
 
 #include "freadln.h"
 
-int freadln(char** output, size_t* length_out) {
+int freadln(FILE* f, char** output, size_t* length_out) {
 	/*
 	 * The length of STDIN line is counted without any terminating characters.
 	 *
@@ -24,7 +23,7 @@ int freadln(char** output, size_t* length_out) {
 	 * 	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
+	 * 	>= 0: length of read line
 	 */
 
 	if (output == NULL)
@@ -41,7 +40,7 @@ int freadln(char** output, size_t* length_out) {
 		return freadln_ERROR;
 
 	int character;
-	while ((character = fgetc(stdin)) != EOF
+	while ((character = fgetc(f)) != EOF
 	       /* stop on a newline character: */ && character != '\n') {
 		(*output)[length] = (char) character;
 
@@ -71,13 +70,40 @@ int freadln(char** output, size_t* length_out) {
 
 #ifdef TEST
 int main(void) {
+	// stdin test
 	printf("Type something> ");
 	char* line;
-	if (freadln(&line, NULL) != freadln_OK) {
+	if (finreadln(&line, NULL) != freadln_OK) {
 		perror("freadln");
 		exit(EXIT_FAILURE);
 	}
 	printf("Input string: '%s'\n", line);
+
+	// file test
+#define TEST_FILE "freadln_test.txt"
+	FILE* f = fopen(TEST_FILE, "w");
+	if (f == NULL) {
+		perror("fopen");
+		exit(EXIT_FAILURE);
+	}
+	fprintf(f, "Hello, world!\nAnother line\n\n");
+	FILE* new_f = freopen(TEST_FILE, "r", f);
+	if (new_f == NULL) {
+		perror("freopen");
+		exit(EXIT_FAILURE);
+	}
+	f = new_f;
+	for (int i = 0; i < 5; i++) {
+		size_t line_length;
+		if (freadln(f, &line, &line_length) != freadln_OK) {
+			perror("freadln");
+			exit(EXIT_FAILURE);
+		}
+		printf("File, line #%d: '%s' (%zu characters)\n", i + 1, line,
+		       line_length);
+	}
+	fclose(f);
+
 	return 0;
 }
 #endif

c-programming/io/freadln.h

@@ -26,6 +26,7 @@ enum freadln_status {
     return freadln_OK;                                                        \
 } while (0)
 
-int freadln(char** output, size_t* length_out);
+int freadln(FILE* f, char** output, size_t* length_out);
+#define finreadln(output, length_out) freadln(stdin, output, length_out)
 
 #endif /* _FREADLN_H */