Add BasicCStringRef to represent a null-termated string (#100)

and use it instead of BasicStringRef in cases that assume that the
string is null-terminated such as POSIX function and format string
parser.

test/format-test.cc

@@ -66,6 +66,7 @@ using fmt::BasicWriter;
 using fmt::format;
 using fmt::FormatError;
 using fmt::StringRef;
+using fmt::CStringRef;
 using fmt::MemoryWriter;
 using fmt::WMemoryWriter;
 using fmt::pad;
@@ -136,6 +137,24 @@ struct WriteChecker {
   EXPECT_PRED_FORMAT1(WriteChecker<wchar_t>(), value)
 }  // namespace
 
+TEST(StringRefTest, Ctor) {
+  EXPECT_STREQ("abc", StringRef("abc").data());
+  EXPECT_EQ(3u, StringRef("abc").size());
+
+  EXPECT_STREQ("defg", StringRef(std::string("defg")).data());
+  EXPECT_EQ(4u, StringRef(std::string("defg")).size());
+}
+
+TEST(StringRefTest, ConvertToString) {
+  std::string s = StringRef("abc").to_string();
+  EXPECT_EQ("abc", s);
+}
+
+TEST(CStringRefTest, Ctor) {
+  EXPECT_STREQ("abc", CStringRef("abc").c_str());
+  EXPECT_STREQ("defg", CStringRef(std::string("defg")).c_str());
+}
+
 class TestString {
  private:
   std::string value_;
@@ -583,7 +602,7 @@ TEST(FormatterTest, ArgErrors) {
 template <int N>
 struct TestFormat {
   template <typename... Args>
-  static std::string format(fmt::StringRef format_str, const Args & ... args) {
+  static std::string format(fmt::CStringRef format_str, const Args & ... args) {
     return TestFormat<N - 1>::format(format_str, N - 1, args...);
   }
 };
@@ -591,7 +610,7 @@ struct TestFormat {
 template <>
 struct TestFormat<0> {
   template <typename... Args>
-  static std::string format(fmt::StringRef format_str, const Args & ... args) {
+  static std::string format(fmt::CStringRef format_str, const Args & ... args) {
     return fmt::format(format_str, args...);
   }
 };
@@ -1372,6 +1391,10 @@ TEST(FormatterTest, FormatStringRef) {
   EXPECT_EQ("test", format("{0}", StringRef("test")));
 }
 
+TEST(FormatterTest, FormatCStringRef) {
+  EXPECT_EQ("test", format("{0}", CStringRef("test")));
+}
+
 TEST(FormatterTest, FormatUsingIOStreams) {
   EXPECT_EQ("a string", format("{0}", TestString("a string")));
   std::string s = format("The date is {0}", Date(2012, 12, 9));
@@ -1440,19 +1463,6 @@ TEST(FormatterTest, FormatExamples) {
   }, error_code, "Cannot open file 'nonexistent'");
 }
 
-TEST(StringRefTest, Ctor) {
-  EXPECT_STREQ("abc", StringRef("abc").c_str());
-  EXPECT_EQ(3u, StringRef("abc").size());
-
-  EXPECT_STREQ("defg", StringRef(std::string("defg")).c_str());
-  EXPECT_EQ(4u, StringRef(std::string("defg")).size());
-}
-
-TEST(StringRefTest, ConvertToString) {
-  std::string s = StringRef("abc").to_string();
-  EXPECT_EQ("abc", s);
-}
-
 TEST(FormatterTest, Examples) {
   EXPECT_EQ("First, thou shalt count to three",
       format("First, thou shalt count to {0}", "three"));

test/posix-mock-test.cc

@@ -207,7 +207,7 @@ int (test::fileno)(FILE *stream) {
 # define EXPECT_EQ_POSIX(expected, actual)
 #endif
 
-void write_file(fmt::StringRef filename, fmt::StringRef content) {
+void write_file(fmt::CStringRef filename, fmt::StringRef content) {
   fmt::BufferedFile f(filename, "w");
   f.print("{}", content);
 }

test/posix-test.cc

@@ -64,7 +64,7 @@ File open_file() {
 // Attempts to write a string to a file.
 void write(File &f, fmt::StringRef s) {
   std::size_t num_chars_left = s.size();
-  const char *ptr = s.c_str();
+  const char *ptr = s.data();
   do {
     std::streamsize count = f.write(ptr, num_chars_left);
     ptr += count;