📝 Added sandbox (code sketchbook)

sandbox/fcntl.c

@@ -0,0 +1,50 @@
+// From Page 84, Chapter 3 of Advanced Programming in the UNIX Environment
+
+#include "apue.h"
+#include <fcntl.h>
+
+int main(int argc, char *argv[]) {
+    int val;
+
+    if (argc !=2)
+        printf("usage: a.out <descriptor#>\n");
+
+    if ((val = fcntl(atoi(argv[1]), F_GETFL, 0)) < 0)
+        printf("fcntl error for fd %d\n", atoi(argv[1]));
+
+    switch (val & O_ACCMODE) {
+        case O_RDONLY:
+            printf("read only\n");
+            break;
+        case O_WRONLY:
+            printf("write only\n");
+            break;
+        case O_RDWR:
+            printf("read write\n");
+            break;
+        default:
+            printf("unknown access mode\n");
+    }
+
+    if (val & O_APPEND)
+        printf(", append\n");
+    if (val & O_NONBLOCK)
+        printf(", nonblocking\n");
+    if (val & O_SYNC)
+        printf(", synchronous writes\n");
+
+#if !defined(_POSIX_C_SOURCE) && defined(O_FSYNC) && (O_FSYNC != O_SYNC)
+    if (val & O_FSYNC)
+        printf(", synchronous writes\n");
+#endif
+
+    putchar('\n');
+    exit(0);
+}
+
+/* EXAMPLE USES:
+ * ./a.out 0 < /dev/tty
+ * ./a.out 1 > temp.foo
+ * ./a.out 2 2>>temp.foo
+ * ./a.out 5 5<>tmep.foo
+ */