Implement an escape mechanism.

format.cc

@@ -23,9 +23,15 @@ enum { PLUS_FLAG = 1, ZERO_FLAG = 2, HEX_PREFIX_FLAG = 4 };
 // FormatError reporting unmatched '{'. The idea is that unmatched '{'
 // should override other errors.
 void ReportError(const char *s, const std::string &message) {
-  while (*s && *s != '}')
-    ++s;
-  throw fmt::FormatError(*s ? message : std::string("unmatched '{' in format"));
+  for (int num_open_braces = 1; *s; ++s) {
+    if (*s == '{') {
+      ++num_open_braces;
+    } else if (*s == '}') {
+      if (--num_open_braces == 0)
+        throw fmt::FormatError(message);
+    }
+  }
+  throw fmt::FormatError("unmatched '{' in format");
 }
 
 void ReportUnknownType(char code, const char *type) {
@@ -225,8 +231,15 @@ void fmt::Formatter::Format() {
   const char *start = format_;
   const char *s = start;
   while (*s) {
-    if (*s++ != '{') continue;
-    // TODO: handle escape sequence
+    char c = *s++;
+    if (c != '{' && c != '}') continue;
+    if (*s == c) {
+      buffer_.insert(buffer_.end(), start, s);
+      start = ++s;
+      continue;
+    }
+    if (c == '}')
+      throw FormatError("unmatched '}' in format");
     buffer_.insert(buffer_.end(), start, s - 1);
 
     // Parse argument index.

format.h

@@ -78,7 +78,7 @@ class Formatter {
     : type(CUSTOM), custom_value(value), format(f) {}
   };
 
-  std::vector<Arg> args_;
+  std::vector<Arg> args_;  // Format arguments.
 
   const char *format_;  // Format string.
 
@@ -94,7 +94,7 @@ class Formatter {
   template <typename T>
   void FormatInt(T value, unsigned flags, int width, char type);
 
-  // Formats a floating point number.
+  // Formats a floating point number (double or long double).
   template <typename T>
   void FormatDouble(
       T value, unsigned flags, int width, int precision, char type);
@@ -127,6 +127,16 @@ class ArgFormatter {
  private:
   friend class Formatter;
 
+  // This method is private to disallow formatting of arbitrary pointers.
+  // If you want to output a pointer cast it to void*. Do not implement!
+  template <typename T>
+  ArgFormatter &operator<<(const T *value);
+
+  // This method is private to disallow formatting of wide characters.
+  // If you want to output a wide character cast it to integer type.
+  // Do not implement!
+  ArgFormatter &operator<<(wchar_t value);
+
  protected:
   mutable Formatter *formatter_;
 
@@ -211,17 +221,6 @@ class ArgFormatter {
     return *this;
   }
 
-  // This method contains a deliberate error to disallow formatting
-  // arbitrary pointers. If you want to output a pointer cast it to void*.
-  template <typename T>
-  ArgFormatter &operator<<(const T *value) {
-    "Formatting arbitrary pointers is not allowed" = value;
-  }
-
-  // This method is not implemented intentionally to disallow formatting
-  // wide characters.
-  ArgFormatter &operator<<(wchar_t value);
-
   template <typename T>
   ArgFormatter &operator<<(T *value) {
     const T *const_value = value;

format_test.cc

@@ -66,8 +66,28 @@ class TestString {
   }
 };
 
+TEST(FormatterTest, Escape) {
+  EXPECT_EQ("{", str(Format("{{")));
+  EXPECT_EQ("before {", str(Format("before {{")));
+  EXPECT_EQ("{ after", str(Format("{{ after")));
+  EXPECT_EQ("before { after", str(Format("before {{ after")));
+
+  EXPECT_EQ("}", str(Format("}}")));
+  EXPECT_EQ("before }", str(Format("before }}")));
+  EXPECT_EQ("} after", str(Format("}} after")));
+  EXPECT_EQ("before } after", str(Format("before }} after")));
+
+  EXPECT_EQ("{}", str(Format("{{}}")));
+  EXPECT_EQ("{42}", str(Format("{{{0}}}") << 42));
+}
+
+TEST(FormatterTest, UnmatchedBraces) {
+  EXPECT_THROW_MSG(Format("{"), FormatError, "unmatched '{' in format");
+  EXPECT_THROW_MSG(Format("}"), FormatError, "unmatched '}' in format");
+  EXPECT_THROW_MSG(Format("{0{}"), FormatError, "unmatched '{' in format");
+}
+
 TEST(FormatterTest, NoArgs) {
-  EXPECT_EQ("abracadabra", str(Format("{0}{1}{0}") << "abra" << "cad"));
   EXPECT_EQ("test", str(Format("test")));
 }
 
@@ -77,7 +97,8 @@ TEST(FormatterTest, ArgsInDifferentPositions) {
   EXPECT_EQ("42 after", str(Format("{0} after") << 42));
   EXPECT_EQ("before 42 after", str(Format("before {0} after") << 42));
   EXPECT_EQ("answer = 42", str(Format("{0} = {1}") << "answer" << 42));
-  EXPECT_EQ("42 is the answer", str(Format("{1} is the {0}") << "answer" << 42));
+  EXPECT_EQ("42 is the answer",
+      str(Format("{1} is the {0}") << "answer" << 42));
   EXPECT_EQ("abracadabra", str(Format("{0}{1}{0}") << "abra" << "cad"));
 }
 
@@ -424,5 +445,3 @@ TEST(FormatterTest, FormatStringFromSpeedTest) {
           << 1.234 << 42 << 3.13 << "str"
           << reinterpret_cast<void*>(1000) << 'X'));
 }
-
-// TODO: more tests