Add doc example for `OsString::reserve_exact`.

diff --git a/src/libstd/ffi/os_str.rs b/src/libstd/ffi/os_str.rs
index bdd8ce5e6d8543ead8bb6e4ba98dc6096dfaf91f..d960d76146fe967e3f3b1bc5b62ef396adac005c 100644 (file)
--- a/src/libstd/ffi/os_str.rs
+++ b/src/libstd/ffi/os_str.rs
@@ -210,6 +210,16 @@ pub fn reserve(&mut self, additional: usize) {
     /// Note that the allocator may give the collection more space than it
     /// requests. Therefore capacity can not be relied upon to be precisely
     /// minimal. Prefer reserve if future insertions are expected.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::ffi::OsString;
+    ///
+    /// let mut s = OsString::new();
+    /// s.reserve_exact(10);
+    /// assert!(s.capacity() >= 10);
+    /// ```
     #[stable(feature = "osstring_simple_functions", since = "1.9.0")]
     pub fn reserve_exact(&mut self, additional: usize) {
         self.inner.reserve_exact(additional)