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diff --git a/stdio/printf.c b/stdio/printf.c
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+/*-*- 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/stdio/stdio.h"
+
+/**
+ * Formats and writes string to stdout.
+ *
+ * Cosmopolitan supports most of the standard formatting behaviors
+ * described by `man 3 printf`, in addition to the following:
+ *
+ * - `%jd`, `%jx`, etc. are {,u}intmax_t which in Cosmopolitan is 128-bit.
+ *
+ * - `%'d` or `%,d` may be used to insert thousands separators. The prior is
+ *   consistent with C; the latter is consistent with Python.
+ *
+ * - `%m` inserts strerror(errno) into the formatted output. This is
+ *   consistent with glibc, musl, and uclibc.
+ *
+ * - `%n` inserts "\n" on non-Windows and "\r\n" on Windows. This is the
+ *   same behavior as Java. It's incompatible with glibc's behavior,
+ *   since that's problematic according to Android's security team.
+ *
+ * - `%hs` converts UTF-16/UCS-2 → UTF-8, which can be helpful on Windows.
+ *   Formatting (e.g. %-10hs) will use monospace display width rather
+ *   than string length or codepoint count.
+ *
+ * - `%ls` (or `%Ls`) converts UTF-32 → UTF-8. Formatting (e.g. %-10ls)
+ *   will use monospace display width rather than string length.
+ *
+ * - The `%#s` and `%#c` alternate forms display values using the
+ *   standard IBM standard 256-letter alphabet. Using `%#.*s` to specify
+ *   length will allow true binary (i.e. with NULs) to be formatted.
+ *
+ * - The `%'s` and `%'c` alternate forms are Cosmopolitan extensions for
+ *   escaping string literals for C/C++ and Python. The outer quotation
+ *   marks can be added automatically using ``%`s``. If constexpr format
+ *   strings are used, we can avoid linking cescapec() too.
+ *
+ * - The backtick modifier (``%`s`` and ``%`c``) and repr() directive
+ *   (`%r`) both ask the formatting machine to represent values as real
+ *   code rather than using arbitrary traditions for displaying values.
+ *   This means it implies the quoting modifier, wraps the value with
+ *   {,u,L}['"] quotes, displays NULL as "NULL" rather than "(null)".
+ *
+ * @see __fmt() for intuitive reference documentation
+ * @see {,v}{,s{,n},{,{,x}as},f,d}printf
+ */
+int(printf)(const char* fmt, ...) {
+  int rc;
+  va_list va;
+  va_start(va, fmt);
+  rc = (vfprintf)(stdout, fmt, va);
+  va_end(va);
+  return rc;
+}