revb: reverse all stdin (bufferred)

1 files changed, 52 insertions, 0 deletions

diff --git a/revb.c b/revb.c
new file mode 100644
index 0000000..d4c47e4
--- /dev/null
+++ b/revb.c
@@ -0,0 +1,52 @@
+/*
+ * Print stdin fully reversed. Unlike util-linux rev(1), this program does not
+ * reverse lines, but buffers everything fully and then writes it on the end.
+ * Author: Peter Wu <lekensteyn@gmail.com>
+ * Date: 2012-11-07
+ */
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#define READ_BLOCK 1024
+#define SIZE_INC (4 * READ_BLOCK)
+
+int main(void) {
+	unsigned len = 0; /* length of data */
+	unsigned str_size = SIZE_INC; /* size of buffer */
+	char *str = malloc(str_size);
+	if (!str) {
+		perror("malloc");
+		return 1;
+	}
+	int n = 0;
+	do {
+		if (str_size - len < SIZE_INC) {
+			str_size += SIZE_INC;
+			str = realloc(str, str_size);
+			if (!str) {
+				fprintf(stderr, "Failed to enlarge buffer to %u: %s\n", str_size, strerror(errno));
+				abort();
+			}
+		}
+		n = read(STDIN_FILENO, str + len, READ_BLOCK);
+		if (n < 0) {
+			perror("read");
+			goto free_str;
+		} else if (n) {
+			len += n;
+		}
+	} while (n);
+
+	/* print in reverse */
+	while (len)
+		putchar(str[--len]);
+
+	free(str);
+	return 0;
+free_str:
+	free(str);
+	return 1;
+}