Implement P0457R2: 'String Prefix and Suffix Checking' for c++2a

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@319687 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/basic.string/string.starts_with/starts_with.ptr.pass.cpp

@@ -0,0 +1,62 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// <string>
+
+//   bool starts_with(const CharT *x) const;
+
+#include <string>
+#include <cassert>
+
+#include "test_macros.h"
+
+int main()
+{
+    {
+    typedef std::string S;
+    const char *s = "abcde";
+    S  s0 {};
+    S  s1 { s, 1 };
+    S  s2 { s, 2 };
+//     S  s3 { s, 3 };
+//     S  s4 { s, 4 };
+//     S  s5 { s, 5 };
+    S  sNot {"def", 3 };
+
+    LIBCPP_ASSERT_NOEXCEPT(s0.starts_with(""));
+
+    assert ( s0.starts_with(""));
+    assert (!s0.starts_with("a"));
+
+    assert ( s1.starts_with(""));
+    assert ( s1.starts_with("a"));
+    assert (!s1.starts_with("ab"));
+    assert (!s1.starts_with("abc"));
+    assert (!s1.starts_with("abcd"));
+    assert (!s1.starts_with("abcde"));
+    assert (!s1.starts_with("def"));
+
+    assert ( s2.starts_with(""));
+    assert ( s2.starts_with("a"));
+    assert ( s2.starts_with("ab"));
+    assert (!s2.starts_with("abc"));
+    assert (!s2.starts_with("abcd"));
+    assert (!s2.starts_with("abcde"));
+    assert (!s2.starts_with("def"));
+
+    assert ( sNot.starts_with(""));
+    assert (!sNot.starts_with("a"));
+    assert (!sNot.starts_with("ab"));
+    assert (!sNot.starts_with("abc"));
+    assert (!sNot.starts_with("abcd"));
+    assert (!sNot.starts_with("abcde"));
+    assert ( sNot.starts_with("def"));
+    }
+}