From 5548e692260c7d468294e5eccbeb63c3a829ee94 Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Tue, 26 May 2020 10:33:40 +0200
Subject: [PATCH] Add working example for E0617 explanation

---
 src/librustc_error_codes/error_codes/E0617.md | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/librustc_error_codes/error_codes/E0617.md b/src/librustc_error_codes/error_codes/E0617.md
index f4357ff755e..61b56766c26 100644
--- a/src/librustc_error_codes/error_codes/E0617.md
+++ b/src/librustc_error_codes/error_codes/E0617.md
@@ -17,3 +17,14 @@ Certain Rust types must be cast before passing them to a variadic function,
 because of arcane ABI rules dictated by the C standard. To fix the error,
 cast the value to the type specified by the error message (which you may need
 to import from `std::os::raw`).
+
+In this case, `c_double` has the same size as `f64` so we can use it directly:
+
+```no_run
+# extern {
+#     fn printf(c: *const i8, ...);
+# }
+unsafe {
+    printf(::std::ptr::null(), 0f64); // ok!
+}
+```