diff --git a/README.md b/README.md
index 6dbb8e827f395061e92a4a379e6941d86c43ae94..cb1cad63945c9e71f46dc0fadcbcc8aee13bc9d7 100644
--- a/README.md
+++ b/README.md
@@ -47,6 +47,7 @@ TinySTL
 	* unordered_set：100%
 	* unique_ptr：100%
 	* shared_ptr：100%
+	* cow_ptr：100%
 * STL Algorithms:  
     * fill：100% 
     * fill_n：100% 
@@ -563,6 +564,23 @@ TinySTL
 
 	up.reset(new string("hello"));
 	assert(*up == "hello");
+
+
+
+####(19):cow_ptr
+
+    cow_ptr<string> cp1(new string("zouxiaohang"));
+	auto cp2 = cp1, cp3 = cp1;
+	assert(cp1 == cp2 && cp2 == cp3);
+	assert(*cp1 == *cp2 && *cp2 == *cp3 && *cp3 == "zouxiaohang");
+
+	*cp2;//read
+	assert(cp1 == cp2 && cp2 == cp3);
+	assert(*cp1 == *cp2 && *cp2 == *cp3 && *cp3 == "zouxiaohang");
+
+	cp2->append(" C++");//write
+	assert(*cp1 == *cp3 && *cp3 == "zouxiaohang");
+	assert(*cp2 == "zouxiaohang C++");
     
  
     
diff --git a/TinySTL/Test/COWPtrTest.cpp b/TinySTL/Test/COWPtrTest.cpp
index 139c1f44cdf21160106fb24547132fe671fe31d6..08667aa2d472e2a903baafe9304a62f573ea8e1a 100644
--- a/TinySTL/Test/COWPtrTest.cpp
+++ b/TinySTL/Test/COWPtrTest.cpp
@@ -20,12 +20,31 @@ namespace TinySTL{
 
 			assert(cp1 == cp2 && !(cp2 != cp3));
 
+			*cp1 = "zouxiaohang";
+			assert(*cp1 == "zouxiaohang");
+			assert(*cp2 == "hello" && *cp3 == "hello");
+
 			cow_ptr<string> cp4;
 			assert(cp4 == nullptr);
 		}
+		void testCase2(){
+			cow_ptr<string> cp1(new string("zouxiaohang"));
+			auto cp2 = cp1, cp3 = cp1;
+			assert(cp1 == cp2 && cp2 == cp3);
+			assert(*cp1 == *cp2 && *cp2 == *cp3 && *cp3 == "zouxiaohang");
+
+			*cp2;//read
+			assert(cp1 == cp2 && cp2 == cp3);
+			assert(*cp1 == *cp2 && *cp2 == *cp3 && *cp3 == "zouxiaohang");
+
+			cp2->append(" C++");//write
+			assert(*cp1 == *cp3 && *cp3 == "zouxiaohang");
+			assert(*cp2 == "zouxiaohang C++");
+		}
 
 		void testAllCases(){
 			testCase1();
+			testCase2();
 		}
 	}
 }
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diff --git a/TinySTL/main.cpp b/TinySTL/main.cpp
index 4c8bd6045237ef05c2b9ea16f33388ee273b8868..ebb5f91b9ad8c09c89a569775284ac2ca853d49a 100644
--- a/TinySTL/main.cpp
+++ b/TinySTL/main.cpp
@@ -26,6 +26,8 @@
 #include "Test\VectorTest.h"
 
 using namespace TinySTL::Profiler;
+#include <string>
+#include <type_traits>
 
 int main(){
 	TinySTL::AlgorithmTest::testAllCases();
@@ -50,6 +52,10 @@ int main(){
 	TinySTL::Unordered_setTest::testAllCases();
 	TinySTL::VectorTest::testAllCases();
 
+	std::string s;
+	if (std::is_const<decltype(s.cbegin())>::value){
+		std::cout << "const" << std::endl;
+	}
 	system("pause");
 	return 0;
 }
\ No newline at end of file