1 files changed, 60 insertions, 0 deletions
diff --git a/stdio/freopen.c b/stdio/freopen.c
new file mode 100644
index 0000000..2f83742
--- /dev/null
+++ b/stdio/freopen.c
@@ -0,0 +1,60 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/stdio/stdio.h"
+#include "libc/sysv/consts/f.h"
+#include "libc/sysv/consts/fd.h"
+#include "libc/sysv/consts/o.h"
+
+/**
+ * Overwrites existing stream.
+ *
+ * This function can be used in two ways. The first is sort of a
+ * mutating assignment. The second behavior, if pathname is NULL, is
+ * just changing the mode of an already open file descriptor.
+ *
+ * @param pathname is the file to open or NULL
+ * @param mode is the mode string flags, see fopenflags()
+ * @param stream is the existing allocated stream memory, which is
+ *     flushed and closed if already open
+ * @return stream object if successful, or NULL w/ errno
+ */
+FILE *freopen(const char *pathname, const char *mode, FILE *stream) {
+  int fd;
+  unsigned flags;
+  flags = fopenflags(mode);
+  fflush(stream);
+  if (pathname) {
+    /* open new stream, overwriting existing alloc */
+    if ((fd = open(pathname, flags, 0666)) != -1) {
+      dup3(fd, stream->fd, flags & O_CLOEXEC);
+      close(fd);
+      stream->iomode = flags;
+      stream->beg = 0;
+      stream->end = 0;
+      return stream;
+    } else {
+      return NULL;
+    }
+  } else {
+    fcntl(stream->fd, F_SETFD, !!(flags & O_CLOEXEC));
+    fcntl(stream->fd, F_SETFL, flags & ~O_CLOEXEC);
+    return stream;
+  }
+}