Add StringRef::{substr, startswith}.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76559 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/StringRef.h

@@ -14,6 +14,7 @@
 #include <string>
 
 namespace llvm {
+
   /// StringRef - Represent a constant reference to a string, i.e. a character
   /// array and a length, which need not be null terminated.
   ///
@@ -24,13 +25,14 @@ namespace llvm {
   class StringRef {
   public:
     typedef const char *iterator;
+    static const size_t npos = std::string::npos;
 
   private:
     /// The start of the string, in an external buffer.
     const char *Data;
 
     /// The length of the string.
-    unsigned Length;
+    size_t Length;
 
   public:
     /// @name Constructors
@@ -120,8 +122,32 @@ namespace llvm {
       return str();
     }
 
+    /// @}
+    /// @name Utility Functions
+    /// @{
+
+    /// substr - Return a reference to a substring of this object.
+    ///
+    /// \param Start - The index of the starting character in the substring; if
+    /// the index is greater than the length of the string then the empty
+    /// substring will be returned.
+    ///
+    /// \param N - The number of characters to included in the substring. If N
+    /// exceeds the number of characters remaining in the string, the string
+    /// suffix (starting with \arg Start) will be returned.
+    StringRef substr(size_t Start, size_t N = npos) const {
+      Start = std::min(Start, Length);
+      return StringRef(Data + Start, std::min(N, Length - Start));
+    }
+
+    /// startswith - Check if this string starts with the given \arg Prefix.
+    bool startswith(const StringRef &Prefix) const { 
+      return substr(0, Prefix.Length) == Prefix;
+    }
+
     /// @}
   };
+
 }
 
 #endif

unittests/ADT/StringRefTest.cpp

@@ -56,4 +56,16 @@ TEST(StringRefTest, Operators) {
   EXPECT_EQ('a', StringRef("aab")[1]);
 }
 
+TEST(StringRefTest, Utilities) {
+  StringRef Str("hello");
+  EXPECT_TRUE(Str.substr(3) == "lo");
+  EXPECT_TRUE(Str.substr(100) == "");
+  EXPECT_TRUE(Str.substr(0, 100) == "hello");
+  EXPECT_TRUE(Str.substr(4, 10) == "o");
+
+  EXPECT_TRUE(Str.startswith("he"));
+  EXPECT_FALSE(Str.startswith("helloworld"));
+  EXPECT_FALSE(Str.startswith("hi"));
+}
+
 } // end anonymous namespace