CPP: Adding GetNddPrefixForRegion for libphonenumber.

cpp/src/phonenumberutil.cc

@@ -777,6 +777,23 @@ void PhoneNumberUtil::GetSupportedRegions(set<string>* regions) const {
   }
 }
 
+void PhoneNumberUtil::GetNddPrefixForRegion(const string& region_code,
+                                            bool strip_non_digits,
+                                            string* national_prefix) const {
+  DCHECK(national_prefix);
+  if (!IsValidRegionCode(region_code)) {
+    logger->Error("Invalid region code provided.");
+    return;
+  }
+  const PhoneMetadata* metadata = GetMetadataForRegion(region_code);
+  national_prefix->assign(metadata->national_prefix());
+  if (strip_non_digits) {
+    // Note: if any other non-numeric symbols are ever used in national
+    // prefixes, these would have to be removed here as well.
+    strrmm(national_prefix, "~");
+  }
+}
+
 bool PhoneNumberUtil::IsValidRegionCode(const string& region_code) const {
   return (region_to_metadata_map_->find(region_code) !=
           region_to_metadata_map_->end());
@@ -951,7 +968,6 @@ void PhoneNumberUtil::FormatOutOfCountryCallingNumber(
     const string& calling_from,
     string* formatted_number) const {
   DCHECK(formatted_number);
-
   if (!IsValidRegionCode(calling_from)) {
     logger->Info("Trying to format number from invalid region. International"
         " formatting applied.");

cpp/src/phonenumberutil.h

@@ -564,6 +564,18 @@ class PhoneNumberUtil {
   // Gets all the supported regions.
   void GetSupportedRegions(set<string>* regions) const;
 
+  // Returns the national dialling prefix for a specific region. For example,
+  // this would be 1 for the United States, and 0 for New Zealand. Set
+  // stripNonDigits to true to strip symbols like "~" (which indicates a wait
+  // for a dialling tone) from the prefix returned. If no national prefix is
+  // present, we return an empty string.
+  //
+  // Set strip_non_digits to true to strip non-digits from the national
+  // dialling prefix.
+  void GetNddPrefixForRegion(const string& region_code,
+                             bool strip_non_digits,
+                             string* national_prefix) const;
+
   // Helper function to check region code is not unknown or null.
   //
   // The region_code parameter is an ISO 3166-1 two-letter country code string.

cpp/src/phonenumberutil_test.cc

@@ -211,6 +211,14 @@ class PhoneNumberUtilTest : public testing::Test {
                                                phone_number);
   }
 
+  void GetNddPrefixForRegion(const string& region,
+                             bool strip_non_digits,
+                             string* ndd_prefix) const {
+    // For testing purposes, we check this is empty first.
+    ndd_prefix->clear();
+    phone_util_.GetNddPrefixForRegion(region, strip_non_digits, ndd_prefix);
+  }
+
   static bool Equals(const PhoneNumberDesc& expected_number,
                      const PhoneNumberDesc& actual_number) {
     return ExactlySameAs(expected_number, actual_number);
@@ -1581,6 +1589,35 @@ TEST_F(PhoneNumberUtilTest, GetCountryCodeForRegion) {
   EXPECT_EQ(0, phone_util_.GetCountryCodeForRegion(RegionCode::CS()));
 }
 
+TEST_F(PhoneNumberUtilTest, GetNationalDiallingPrefixForRegion) {
+  string ndd_prefix;
+  GetNddPrefixForRegion(RegionCode::US(), false, &ndd_prefix);
+  EXPECT_EQ("1", ndd_prefix);
+
+  // Test non-main country to see it gets the national dialling prefix for the
+  // main country with that country calling code.
+  GetNddPrefixForRegion(RegionCode::BS(), false, &ndd_prefix);
+  EXPECT_EQ("1", ndd_prefix);
+
+  GetNddPrefixForRegion(RegionCode::NZ(), false, &ndd_prefix);
+  EXPECT_EQ("0", ndd_prefix);
+
+  // Test case with non digit in the national prefix.
+  GetNddPrefixForRegion(RegionCode::AO(), false, &ndd_prefix);
+  EXPECT_EQ("0~0", ndd_prefix);
+
+  GetNddPrefixForRegion(RegionCode::AO(), true, &ndd_prefix);
+  EXPECT_EQ("00", ndd_prefix);
+
+  // Test cases with invalid regions.
+  GetNddPrefixForRegion(RegionCode::ZZ(), false, &ndd_prefix);
+  EXPECT_EQ("", ndd_prefix);
+
+  // CS is already deprecated so the library doesn't support it.
+  GetNddPrefixForRegion(RegionCode::CS(), false, &ndd_prefix);
+  EXPECT_EQ("", ndd_prefix);
+}
+
 TEST_F(PhoneNumberUtilTest, IsViablePhoneNumber) {
   // Only one or two digits before strange non-possible punctuation.
   EXPECT_FALSE(IsViablePhoneNumber("12. March"));