Added the 'at' method to string.

3 files changed, 35 insertions, 0 deletions

diff --git a/include/string b/include/string
index 8e1ebbe..7c2f474 100644
--- a/include/string
+++ b/include/string
@@ -193,6 +193,10 @@ class string
     // @return a reference to the char.
     char& operator[](const size_type pos);
 
+    // 'at' is similar to operator[] except that it does check bounds.
+    const char& at(const size_type pos) const;
+    char& at(const size_type pos);
+
     // Assignments.
     string& operator=(const string& str) { return assign(str); }
     string& operator=(const char* str) { return assign(str); }
diff --git a/src/string.cpp b/src/string.cpp
index e1c4cf9..d0361e6 100644
--- a/src/string.cpp
+++ b/src/string.cpp
@@ -39,6 +39,9 @@
 
 namespace {
 char kEmptyString[1] = { '\0' };
+// Dummy char used in the 'at' accessor when the index is out of
+// range.
+char sDummy;
 }
 
 namespace std {
@@ -446,6 +449,26 @@ char& string::operator[](const size_type pos)
     return mData[pos];
 }
 
+const char& string::at(const size_type pos) const
+{
+    if (pos < mLength) {
+        return mData[pos];
+    } else {
+        sDummy = 'X';
+        return sDummy;
+    }
+}
+
+char& string::at(const size_type pos)
+{
+    if (pos < mLength) {
+        return mData[pos];
+    } else {
+        sDummy = 'X';
+        return sDummy;
+    }
+}
+
 string& string::assign(const string& str)
 {
     clear();
diff --git a/tests/test_string.cpp b/tests/test_string.cpp
index 60c02aa..337d879 100644
--- a/tests/test_string.cpp
+++ b/tests/test_string.cpp
@@ -542,6 +542,14 @@ bool testAccessor()
     str05.reserve(100);
     str05[99] = 'a';
 
+    // 'at'
+    EXPECT_TRUE(str01.at(0) == 'E');
+    EXPECT_TRUE(str01.at(7) == 'S');
+    EXPECT_TRUE(str01.at(8) == 'X');  // 'X' is the dummy value returned.
+
+    str01.at(1) = 'A';
+    str01.at(6) = 'K';
+    EXPECT_TRUE(str01 == "EArmarKS");
     return true;
 }