Add sprintf overload for wide strings

and fix an issue in formatting user-defined objects.
Thanks to @ScottLangham

format.cc

@@ -526,7 +526,8 @@ class PrintfArgFormatter :
 
   void visit_custom(Arg::CustomValue c) {
     BasicFormatter<Char> formatter(ArgList(), this->writer());
-    const char *format = "}";
+    const Char format_str[] = {'}', 0};
+    const Char *format = format_str;
     c.format(&formatter, c.value, &format);
   }
 };

format.h

@@ -2706,6 +2706,12 @@ inline std::string sprintf(CStringRef format, ArgList args) {
   return w.str();
 }
 
+inline std::wstring sprintf(WCStringRef format, ArgList args) {
+  WMemoryWriter w;
+  printf(w, format, args);
+  return w.str();
+}
+
 /**
   \rst
   Prints formatted data to the file *f*.
@@ -2994,6 +3000,7 @@ FMT_VARIADIC(void, print, std::FILE *, CStringRef)
 FMT_VARIADIC(void, print, std::ostream &, CStringRef)
 FMT_VARIADIC(void, print_colored, Color, CStringRef)
 FMT_VARIADIC(std::string, sprintf, CStringRef)
+FMT_VARIADIC_W(std::wstring, sprintf, WCStringRef)
 FMT_VARIADIC(int, printf, CStringRef)
 FMT_VARIADIC(int, fprintf, std::FILE *, CStringRef)
 }

test/printf-test.cc

@@ -456,3 +456,7 @@ TEST(PrintfTest, PrintfError) {
   EXPECT_LT(result, 0);
 }
 #endif
+
+TEST(PrintfTest, WideString) {
+  EXPECT_EQ(L"abc", fmt::sprintf(L"%s", TestWString(L"abc")));
+}

test/util.h

@@ -68,15 +68,25 @@ inline FILE *safe_fopen(const char *filename, const char *mode) {
 #endif
 }
 
-class TestString {
+template <typename Char>
+class BasicTestString {
  private:
-  std::string value_;
+  std::basic_string<Char> value_;
+
+  static const Char EMPTY[];
 
  public:
-  explicit TestString(const char *value = "") : value_(value) {}
+  explicit BasicTestString(const Char *value = EMPTY) : value_(value) {}
 
-  friend std::ostream &operator<<(std::ostream &os, const TestString &s) {
+  friend std::basic_ostream<Char> &operator<<(
+      std::basic_ostream<Char> &os, const BasicTestString &s) {
     os << s.value_;
     return os;
   }
 };
+
+template <typename Char>
+const Char BasicTestString<Char>::EMPTY[] = {0};
+
+typedef BasicTestString<char> TestString;
+typedef BasicTestString<wchar_t> TestWString;