Implemented #335: custom printf support

fmt/CMakeLists.txt

@@ -1,6 +1,7 @@
 # Define the fmt library, its includes and the needed defines.
 # format.cc is added to FMT_HEADERS for the header-only configuration.
-set(FMT_HEADERS format.h format.cc ostream.h ostream.cc string.h time.h)
+set(FMT_HEADERS format.h format.cc ostream.h ostream.cc printf.h
+                string.h time.h)
 if (HAVE_OPEN)
   set(FMT_HEADERS ${FMT_HEADERS} posix.h)
   set(FMT_SOURCES ${FMT_SOURCES} posix.cc)

fmt/format.cc

@@ -26,6 +26,7 @@
  */
 
 #include "fmt/format.h"
+#include "fmt/printf.h"
 
 #include <string.h>
 
@@ -100,27 +101,6 @@ inline int fmt_snprintf(char *buffer, size_t size, const char *format, ...) {
 # define FMT_SWPRINTF swprintf
 #endif // defined(_WIN32) && defined(__MINGW32__) && !defined(__NO_ISOCEXT)
 
-// Checks if a value fits in int - used to avoid warnings about comparing
-// signed and unsigned integers.
-template <bool IsSigned>
-struct IntChecker {
-  template <typename T>
-  static bool fits_in_int(T value) {
-    unsigned max = INT_MAX;
-    return value <= max;
-  }
-  static bool fits_in_int(bool) { return true; }
-};
-
-template <>
-struct IntChecker<true> {
-  template <typename T>
-  static bool fits_in_int(T value) {
-    return value >= INT_MIN && value <= INT_MAX;
-  }
-  static bool fits_in_int(int) { return true; }
-};
-
 const char RESET_COLOR[] = "\x1b[0m";
 
 typedef void (*FormatFunc)(Writer &, int, StringRef);
@@ -225,136 +205,6 @@ void report_error(FormatFunc func, int error_code,
   std::fwrite(full_message.data(), full_message.size(), 1, stderr);
   std::fputc('\n', stderr);
 }
-
-// IsZeroInt::visit(arg) returns true iff arg is a zero integer.
-class IsZeroInt : public ArgVisitor<IsZeroInt, bool> {
- public:
-  template <typename T>
-  bool visit_any_int(T value) { return value == 0; }
-};
-
-// Checks if an argument is a valid printf width specifier and sets
-// left alignment if it is negative.
-class WidthHandler : public ArgVisitor<WidthHandler, unsigned> {
- private:
-  FormatSpec &spec_;
-
-  FMT_DISALLOW_COPY_AND_ASSIGN(WidthHandler);
-
- public:
-  explicit WidthHandler(FormatSpec &spec) : spec_(spec) {}
-
-  void report_unhandled_arg() {
-    FMT_THROW(FormatError("width is not integer"));
-  }
-
-  template <typename T>
-  unsigned visit_any_int(T value) {
-    typedef typename internal::IntTraits<T>::MainType UnsignedType;
-    UnsignedType width = static_cast<UnsignedType>(value);
-    if (internal::is_negative(value)) {
-      spec_.align_ = ALIGN_LEFT;
-      width = 0 - width;
-    }
-    if (width > INT_MAX)
-      FMT_THROW(FormatError("number is too big"));
-    return static_cast<unsigned>(width);
-  }
-};
-
-class PrecisionHandler : public ArgVisitor<PrecisionHandler, int> {
- public:
-  void report_unhandled_arg() {
-    FMT_THROW(FormatError("precision is not integer"));
-  }
-
-  template <typename T>
-  int visit_any_int(T value) {
-    if (!IntChecker<std::numeric_limits<T>::is_signed>::fits_in_int(value))
-      FMT_THROW(FormatError("number is too big"));
-    return static_cast<int>(value);
-  }
-};
-
-template <typename T, typename U>
-struct is_same {
-  enum { value = 0 };
-};
-
-template <typename T>
-struct is_same<T, T> {
-  enum { value = 1 };
-};
-
-// An argument visitor that converts an integer argument to T for printf,
-// if T is an integral type. If T is void, the argument is converted to
-// corresponding signed or unsigned type depending on the type specifier:
-// 'd' and 'i' - signed, other - unsigned)
-template <typename T = void>
-class ArgConverter : public ArgVisitor<ArgConverter<T>, void> {
- private:
-  internal::Arg &arg_;
-  wchar_t type_;
-
-  FMT_DISALLOW_COPY_AND_ASSIGN(ArgConverter);
-
- public:
-  ArgConverter(internal::Arg &arg, wchar_t type)
-    : arg_(arg), type_(type) {}
-
-  void visit_bool(bool value) {
-    if (type_ != 's')
-      visit_any_int(value);
-  }
-
-  template <typename U>
-  void visit_any_int(U value) {
-    bool is_signed = type_ == 'd' || type_ == 'i';
-    using internal::Arg;
-    typedef typename internal::Conditional<
-        is_same<T, void>::value, U, T>::type TargetType;
-    if (sizeof(TargetType) <= sizeof(int)) {
-      // Extra casts are used to silence warnings.
-      if (is_signed) {
-        arg_.type = Arg::INT;
-        arg_.int_value = static_cast<int>(static_cast<TargetType>(value));
-      } else {
-        arg_.type = Arg::UINT;
-        typedef typename internal::MakeUnsigned<TargetType>::Type Unsigned;
-        arg_.uint_value = static_cast<unsigned>(static_cast<Unsigned>(value));
-      }
-    } else {
-      if (is_signed) {
-        arg_.type = Arg::LONG_LONG;
-        // glibc's printf doesn't sign extend arguments of smaller types:
-        //   std::printf("%lld", -42);  // prints "4294967254"
-        // but we don't have to do the same because it's a UB.
-        arg_.long_long_value = static_cast<LongLong>(value);
-      } else {
-        arg_.type = Arg::ULONG_LONG;
-        arg_.ulong_long_value =
-            static_cast<typename internal::MakeUnsigned<U>::Type>(value);
-      }
-    }
-  }
-};
-
-// Converts an integer argument to char for printf.
-class CharConverter : public ArgVisitor<CharConverter, void> {
- private:
-  internal::Arg &arg_;
-
-  FMT_DISALLOW_COPY_AND_ASSIGN(CharConverter);
-
- public:
-  explicit CharConverter(internal::Arg &arg) : arg_(arg) {}
-
-  template <typename T>
-  void visit_any_int(T value) {
-    arg_.type = internal::Arg::CHAR;
-    arg_.int_value = static_cast<char>(value);
-  }
-};
 }  // namespace
 
 namespace internal {
@@ -365,75 +215,6 @@ FMT_FUNC void format_system_error(
   Writer &out, int error_code, StringRef message) FMT_NOEXCEPT {
   fmt::format_system_error(out, error_code, message);
 }
-
-template <typename Char>
-class PrintfArgFormatter :
-    public ArgFormatterBase<PrintfArgFormatter<Char>, Char> {
-
-  void write_null_pointer() {
-    this->spec().type_ = 0;
-    this->write("(nil)");
-  }
-
-  typedef ArgFormatterBase<PrintfArgFormatter<Char>, Char> Base;
-
- public:
-  PrintfArgFormatter(BasicWriter<Char> &w, FormatSpec &s)
-  : ArgFormatterBase<PrintfArgFormatter<Char>, Char>(w, s) {}
-
-  void visit_bool(bool value) {
-    FormatSpec &fmt_spec = this->spec();
-    if (fmt_spec.type_ != 's')
-      return this->visit_any_int(value);
-    fmt_spec.type_ = 0;
-    this->write(value);
-  }
-
-  void visit_char(int value) {
-    const FormatSpec &fmt_spec = this->spec();
-    BasicWriter<Char> &w = this->writer();
-    if (fmt_spec.type_ && fmt_spec.type_ != 'c')
-      w.write_int(value, fmt_spec);
-    typedef typename BasicWriter<Char>::CharPtr CharPtr;
-    CharPtr out = CharPtr();
-    if (fmt_spec.width_ > 1) {
-      Char fill = ' ';
-      out = w.grow_buffer(fmt_spec.width_);
-      if (fmt_spec.align_ != ALIGN_LEFT) {
-        std::fill_n(out, fmt_spec.width_ - 1, fill);
-        out += fmt_spec.width_ - 1;
-      } else {
-        std::fill_n(out + 1, fmt_spec.width_ - 1, fill);
-      }
-    } else {
-      out = w.grow_buffer(1);
-    }
-    *out = static_cast<Char>(value);
-  }
-
-  void visit_cstring(const char *value) {
-    if (value)
-      Base::visit_cstring(value);
-    else if (this->spec().type_ == 'p')
-      write_null_pointer();
-    else
-      this->write("(null)");
-  }
-
-  void visit_pointer(const void *value) {
-    if (value)
-      return Base::visit_pointer(value);
-    this->spec().type_ = 0;
-    write_null_pointer();
-  }
-
-  void visit_custom(Arg::CustomValue c) {
-    BasicFormatter<Char> formatter(ArgList(), this->writer());
-    const Char format_str[] = {'}', 0};
-    const Char *format = format_str;
-    c.format(&formatter, c.value, &format);
-  }
-};
 }  // namespace internal
 }  // namespace fmt
 
@@ -686,178 +467,6 @@ FMT_FUNC Arg fmt::internal::FormatterBase::do_get_arg(
   return arg;
 }
 
-template <typename Char>
-void fmt::internal::PrintfFormatter<Char>::parse_flags(
-    FormatSpec &spec, const Char *&s) {
-  for (;;) {
-    switch (*s++) {
-      case '-':
-        spec.align_ = ALIGN_LEFT;
-        break;
-      case '+':
-        spec.flags_ |= SIGN_FLAG | PLUS_FLAG;
-        break;
-      case '0':
-        spec.fill_ = '0';
-        break;
-      case ' ':
-        spec.flags_ |= SIGN_FLAG;
-        break;
-      case '#':
-        spec.flags_ |= HASH_FLAG;
-        break;
-      default:
-        --s;
-        return;
-    }
-  }
-}
-
-template <typename Char>
-Arg fmt::internal::PrintfFormatter<Char>::get_arg(
-    const Char *s, unsigned arg_index) {
-  (void)s;
-  const char *error = 0;
-  Arg arg = arg_index == UINT_MAX ?
-    next_arg(error) : FormatterBase::get_arg(arg_index - 1, error);
-  if (error)
-    FMT_THROW(FormatError(!*s ? "invalid format string" : error));
-  return arg;
-}
-
-template <typename Char>
-unsigned fmt::internal::PrintfFormatter<Char>::parse_header(
-  const Char *&s, FormatSpec &spec) {
-  unsigned arg_index = UINT_MAX;
-  Char c = *s;
-  if (c >= '0' && c <= '9') {
-    // Parse an argument index (if followed by '$') or a width possibly
-    // preceded with '0' flag(s).
-    unsigned value = parse_nonnegative_int(s);
-    if (*s == '$') {  // value is an argument index
-      ++s;
-      arg_index = value;
-    } else {
-      if (c == '0')
-        spec.fill_ = '0';
-      if (value != 0) {
-        // Nonzero value means that we parsed width and don't need to
-        // parse it or flags again, so return now.
-        spec.width_ = value;
-        return arg_index;
-      }
-    }
-  }
-  parse_flags(spec, s);
-  // Parse width.
-  if (*s >= '0' && *s <= '9') {
-    spec.width_ = parse_nonnegative_int(s);
-  } else if (*s == '*') {
-    ++s;
-    spec.width_ = WidthHandler(spec).visit(get_arg(s));
-  }
-  return arg_index;
-}
-
-template <typename Char>
-void fmt::internal::PrintfFormatter<Char>::format(
-    BasicWriter<Char> &writer, BasicCStringRef<Char> format_str) {
-  const Char *start = format_str.c_str();
-  const Char *s = start;
-  while (*s) {
-    Char c = *s++;
-    if (c != '%') continue;
-    if (*s == c) {
-      write(writer, start, s);
-      start = ++s;
-      continue;
-    }
-    write(writer, start, s - 1);
-
-    FormatSpec spec;
-    spec.align_ = ALIGN_RIGHT;
-
-    // Parse argument index, flags and width.
-    unsigned arg_index = parse_header(s, spec);
-
-    // Parse precision.
-    if (*s == '.') {
-      ++s;
-      if ('0' <= *s && *s <= '9') {
-        spec.precision_ = static_cast<int>(parse_nonnegative_int(s));
-      } else if (*s == '*') {
-        ++s;
-        spec.precision_ = PrecisionHandler().visit(get_arg(s));
-      }
-    }
-
-    Arg arg = get_arg(s, arg_index);
-    if (spec.flag(HASH_FLAG) && IsZeroInt().visit(arg))
-      spec.flags_ &= ~to_unsigned<int>(HASH_FLAG);
-    if (spec.fill_ == '0') {
-      if (arg.type <= Arg::LAST_NUMERIC_TYPE)
-        spec.align_ = ALIGN_NUMERIC;
-      else
-        spec.fill_ = ' ';  // Ignore '0' flag for non-numeric types.
-    }
-
-    // Parse length and convert the argument to the required type.
-    switch (*s++) {
-    case 'h':
-      if (*s == 'h')
-        ArgConverter<signed char>(arg, *++s).visit(arg);
-      else
-        ArgConverter<short>(arg, *s).visit(arg);
-      break;
-    case 'l':
-      if (*s == 'l')
-        ArgConverter<fmt::LongLong>(arg, *++s).visit(arg);
-      else
-        ArgConverter<long>(arg, *s).visit(arg);
-      break;
-    case 'j':
-      ArgConverter<intmax_t>(arg, *s).visit(arg);
-      break;
-    case 'z':
-      ArgConverter<std::size_t>(arg, *s).visit(arg);
-      break;
-    case 't':
-      ArgConverter<std::ptrdiff_t>(arg, *s).visit(arg);
-      break;
-    case 'L':
-      // printf produces garbage when 'L' is omitted for long double, no
-      // need to do the same.
-      break;
-    default:
-      --s;
-      ArgConverter<void>(arg, *s).visit(arg);
-    }
-
-    // Parse type.
-    if (!*s)
-      FMT_THROW(FormatError("invalid format string"));
-    spec.type_ = static_cast<char>(*s++);
-    if (arg.type <= Arg::LAST_INTEGER_TYPE) {
-      // Normalize type.
-      switch (spec.type_) {
-      case 'i': case 'u':
-        spec.type_ = 'd';
-        break;
-      case 'c':
-        // TODO: handle wchar_t
-        CharConverter(arg).visit(arg);
-        break;
-      }
-    }
-
-    start = s;
-
-    // Format argument.
-    internal::PrintfArgFormatter<Char>(writer, spec).visit(arg);
-  }
-  write(writer, start, s);
-}
-
 FMT_FUNC void fmt::report_system_error(
     int error_code, fmt::StringRef message) FMT_NOEXCEPT {
   // 'fmt::' is for bcc32.

fmt/format.h

@@ -1318,8 +1318,8 @@ class RuntimeError : public std::runtime_error {
   RuntimeError() : std::runtime_error("") {}
 };
 
-template <typename Char>
+template <typename Impl, typename Char>
-class PrintfArgFormatter;
+class BasicPrintfArgFormatter;
 
 template <typename Char>
 class ArgMap;
@@ -1937,26 +1937,6 @@ class FormatterBase {
       w << BasicStringRef<Char>(start, internal::to_unsigned(end - start));
   }
 };
-
-// A printf formatter.
-template <typename Char>
-class PrintfFormatter : private FormatterBase {
- private:
-  void parse_flags(FormatSpec &spec, const Char *&s);
-
-  // Returns the argument with specified index or, if arg_index is equal
-  // to the maximum unsigned value, the next argument.
-  Arg get_arg(const Char *s,
-      unsigned arg_index = (std::numeric_limits<unsigned>::max)());
-
-  // Parses argument index, flags and width and returns the argument index.
-  unsigned parse_header(const Char *&s, FormatSpec &spec);
-
- public:
-  explicit PrintfFormatter(const ArgList &args) : FormatterBase(args) {}
-  FMT_API void format(BasicWriter<Char> &writer,
-                      BasicCStringRef<Char> format_str);
-};
 }  // namespace internal
 
 /**
@@ -2420,7 +2400,8 @@ class BasicWriter {
   template <typename Impl, typename Char_>
   friend class internal::ArgFormatterBase;
 
-  friend class internal::PrintfArgFormatter<Char>;
+  template <typename Impl, typename Char_>
+  friend class internal::BasicPrintfArgFormatter;
 
  protected:
   /**
@@ -3187,56 +3168,6 @@ FMT_API void print(std::FILE *f, CStringRef format_str, ArgList args);
  */
 FMT_API void print(CStringRef format_str, ArgList args);
 
-template <typename Char>
-void printf(BasicWriter<Char> &w, BasicCStringRef<Char> format, ArgList args) {
-  internal::PrintfFormatter<Char>(args).format(w, format);
-}
-
-/**
-  \rst
-  Formats arguments and returns the result as a string.
-
-  **Example**::
-
-    std::string message = fmt::sprintf("The answer is %d", 42);
-  \endrst
-*/
-inline std::string sprintf(CStringRef format, ArgList args) {
-  MemoryWriter w;
-  printf(w, format, 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*.
-
-  **Example**::
-
-    fmt::fprintf(stderr, "Don't %s!", "panic");
-  \endrst
- */
-FMT_API int fprintf(std::FILE *f, CStringRef format, ArgList args);
-
-/**
-  \rst
-  Prints formatted data to ``stdout``.
-
-  **Example**::
-
-    fmt::printf("Elapsed time: %.2f seconds", 1.23);
-  \endrst
- */
-inline int printf(CStringRef format, ArgList args) {
-  return fprintf(stdout, format, args);
-}
-
 /**
   Fast integer formatter.
  */
@@ -3502,12 +3433,7 @@ FMT_VARIADIC(std::string, format, CStringRef)
 FMT_VARIADIC_W(std::wstring, format, WCStringRef)
 FMT_VARIADIC(void, print, CStringRef)
 FMT_VARIADIC(void, print, std::FILE *, 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)
 
 namespace internal {
 template <typename Char>

fmt/ostream.cc

@@ -26,6 +26,7 @@
  */
 
 #include "fmt/ostream.h"
+#include "fmt/printf.h"
 
 namespace fmt {
 

fmt/printf.h

@@ -0,0 +1,497 @@
+/*
+ Formatting library for C++
+
+ Copyright (c) 2012 - 2016, Victor Zverovich
+ All rights reserved.
+
+ For the license information refer to format.h.
+ */
+
+#ifndef FMT_PRINTF_H_
+#define FMT_PRINTF_H_
+
+#include <algorithm>  // std::fill_n
+#include <limits>     // std::numeric_limits
+
+#include "fmt/format.h"
+
+namespace fmt {
+namespace internal {
+
+// Checks if a value fits in int - used to avoid warnings about comparing
+// signed and unsigned integers.
+template <bool IsSigned>
+struct IntChecker {
+  template <typename T>
+  static bool fits_in_int(T value) {
+    unsigned max = std::numeric_limits<int>::max();
+    return value <= max;
+  }
+  static bool fits_in_int(bool) { return true; }
+};
+
+template <>
+struct IntChecker<true> {
+  template <typename T>
+  static bool fits_in_int(T value) {
+    return value >= std::numeric_limits<int>::min() &&
+           value <= std::numeric_limits<int>::max();
+  }
+  static bool fits_in_int(int) { return true; }
+};
+
+class PrecisionHandler : public ArgVisitor<PrecisionHandler, int> {
+ public:
+  void report_unhandled_arg() {
+    FMT_THROW(FormatError("precision is not integer"));
+  }
+
+  template <typename T>
+  int visit_any_int(T value) {
+    if (!IntChecker<std::numeric_limits<T>::is_signed>::fits_in_int(value))
+      FMT_THROW(FormatError("number is too big"));
+    return static_cast<int>(value);
+  }
+};
+
+// IsZeroInt::visit(arg) returns true iff arg is a zero integer.
+class IsZeroInt : public ArgVisitor<IsZeroInt, bool> {
+ public:
+  template <typename T>
+  bool visit_any_int(T value) { return value == 0; }
+};
+
+template <typename T, typename U>
+struct is_same {
+  enum { value = 0 };
+};
+
+template <typename T>
+struct is_same<T, T> {
+  enum { value = 1 };
+};
+
+// An argument visitor that converts an integer argument to T for printf,
+// if T is an integral type. If T is void, the argument is converted to
+// corresponding signed or unsigned type depending on the type specifier:
+// 'd' and 'i' - signed, other - unsigned)
+template <typename T = void>
+class ArgConverter : public ArgVisitor<ArgConverter<T>, void> {
+ private:
+  internal::Arg &arg_;
+  wchar_t type_;
+
+  FMT_DISALLOW_COPY_AND_ASSIGN(ArgConverter);
+
+ public:
+  ArgConverter(internal::Arg &arg, wchar_t type)
+    : arg_(arg), type_(type) {}
+
+  void visit_bool(bool value) {
+    if (type_ != 's')
+      visit_any_int(value);
+  }
+
+  template <typename U>
+  void visit_any_int(U value) {
+    bool is_signed = type_ == 'd' || type_ == 'i';
+    using internal::Arg;
+    typedef typename internal::Conditional<
+        is_same<T, void>::value, U, T>::type TargetType;
+    if (sizeof(TargetType) <= sizeof(int)) {
+      // Extra casts are used to silence warnings.
+      if (is_signed) {
+        arg_.type = Arg::INT;
+        arg_.int_value = static_cast<int>(static_cast<TargetType>(value));
+      } else {
+        arg_.type = Arg::UINT;
+        typedef typename internal::MakeUnsigned<TargetType>::Type Unsigned;
+        arg_.uint_value = static_cast<unsigned>(static_cast<Unsigned>(value));
+      }
+    } else {
+      if (is_signed) {
+        arg_.type = Arg::LONG_LONG;
+        // glibc's printf doesn't sign extend arguments of smaller types:
+        //   std::printf("%lld", -42);  // prints "4294967254"
+        // but we don't have to do the same because it's a UB.
+        arg_.long_long_value = static_cast<LongLong>(value);
+      } else {
+        arg_.type = Arg::ULONG_LONG;
+        arg_.ulong_long_value =
+            static_cast<typename internal::MakeUnsigned<U>::Type>(value);
+      }
+    }
+  }
+};
+
+// Converts an integer argument to char for printf.
+class CharConverter : public ArgVisitor<CharConverter, void> {
+ private:
+  internal::Arg &arg_;
+
+  FMT_DISALLOW_COPY_AND_ASSIGN(CharConverter);
+
+ public:
+  explicit CharConverter(internal::Arg &arg) : arg_(arg) {}
+
+  template <typename T>
+  void visit_any_int(T value) {
+    arg_.type = internal::Arg::CHAR;
+    arg_.int_value = static_cast<char>(value);
+  }
+};
+
+// Checks if an argument is a valid printf width specifier and sets
+// left alignment if it is negative.
+class WidthHandler : public ArgVisitor<WidthHandler, unsigned> {
+ private:
+  FormatSpec &spec_;
+
+  FMT_DISALLOW_COPY_AND_ASSIGN(WidthHandler);
+
+ public:
+  explicit WidthHandler(FormatSpec &spec) : spec_(spec) {}
+
+  void report_unhandled_arg() {
+    FMT_THROW(FormatError("width is not integer"));
+  }
+
+  template <typename T>
+  unsigned visit_any_int(T value) {
+    typedef typename internal::IntTraits<T>::MainType UnsignedType;
+    UnsignedType width = static_cast<UnsignedType>(value);
+    if (internal::is_negative(value)) {
+      spec_.align_ = ALIGN_LEFT;
+      width = 0 - width;
+    }
+    if (width > std::numeric_limits<int>::max())
+      FMT_THROW(FormatError("number is too big"));
+    return static_cast<unsigned>(width);
+  }
+};
+
+template <typename Impl, typename Char>
+class BasicPrintfArgFormatter : public ArgFormatterBase<Impl, Char> {
+ private:
+  void write_null_pointer() {
+    this->spec().type_ = 0;
+    this->write("(nil)");
+  }
+
+  typedef ArgFormatterBase<Impl, Char> Base;
+
+ public:
+  BasicPrintfArgFormatter(BasicWriter<Char> &w, FormatSpec &s)
+  : ArgFormatterBase<Impl, Char>(w, s) {}
+
+  void visit_bool(bool value) {
+    FormatSpec &fmt_spec = this->spec();
+    if (fmt_spec.type_ != 's')
+      return this->visit_any_int(value);
+    fmt_spec.type_ = 0;
+    this->write(value);
+  }
+
+  void visit_char(int value) {
+    const FormatSpec &fmt_spec = this->spec();
+    BasicWriter<Char> &w = this->writer();
+    if (fmt_spec.type_ && fmt_spec.type_ != 'c')
+      w.write_int(value, fmt_spec);
+    typedef typename BasicWriter<Char>::CharPtr CharPtr;
+    CharPtr out = CharPtr();
+    if (fmt_spec.width_ > 1) {
+      Char fill = ' ';
+      out = w.grow_buffer(fmt_spec.width_);
+      if (fmt_spec.align_ != ALIGN_LEFT) {
+        std::fill_n(out, fmt_spec.width_ - 1, fill);
+        out += fmt_spec.width_ - 1;
+      } else {
+        std::fill_n(out + 1, fmt_spec.width_ - 1, fill);
+      }
+    } else {
+      out = w.grow_buffer(1);
+    }
+    *out = static_cast<Char>(value);
+  }
+
+  void visit_cstring(const char *value) {
+    if (value)
+      Base::visit_cstring(value);
+    else if (this->spec().type_ == 'p')
+      write_null_pointer();
+    else
+      this->write("(null)");
+  }
+
+  void visit_pointer(const void *value) {
+    if (value)
+      return Base::visit_pointer(value);
+    this->spec().type_ = 0;
+    write_null_pointer();
+  }
+
+  void visit_custom(Arg::CustomValue c) {
+    BasicFormatter<Char> formatter(ArgList(), this->writer());
+    const Char format_str[] = {'}', 0};
+    const Char *format = format_str;
+    c.format(&formatter, c.value, &format);
+  }
+};
+
+/** The default printf argument formatter. */
+template <typename Char>
+class PrintfArgFormatter
+    : public BasicPrintfArgFormatter<PrintfArgFormatter<Char>, Char> {
+ public:
+  /** Constructs an argument formatter object. */
+  PrintfArgFormatter(BasicWriter<Char> &w, FormatSpec &s)
+  : BasicPrintfArgFormatter<PrintfArgFormatter<Char>, Char>(w, s) {}
+};
+
+// A printf formatter.
+template <typename Char, typename ArgFormatter = PrintfArgFormatter<Char> >
+class PrintfFormatter : private FormatterBase {
+ private:
+  void parse_flags(FormatSpec &spec, const Char *&s);
+
+  // Returns the argument with specified index or, if arg_index is equal
+  // to the maximum unsigned value, the next argument.
+  Arg get_arg(const Char *s,
+      unsigned arg_index = (std::numeric_limits<unsigned>::max)());
+
+  // Parses argument index, flags and width and returns the argument index.
+  unsigned parse_header(const Char *&s, FormatSpec &spec);
+
+ public:
+  explicit PrintfFormatter(const ArgList &args) : FormatterBase(args) {}
+  FMT_API void format(BasicWriter<Char> &writer,
+                      BasicCStringRef<Char> format_str);
+};
+
+template <typename Char, typename AF>
+void PrintfFormatter<Char, AF>::parse_flags(FormatSpec &spec, const Char *&s) {
+  for (;;) {
+    switch (*s++) {
+      case '-':
+        spec.align_ = ALIGN_LEFT;
+        break;
+      case '+':
+        spec.flags_ |= SIGN_FLAG | PLUS_FLAG;
+        break;
+      case '0':
+        spec.fill_ = '0';
+        break;
+      case ' ':
+        spec.flags_ |= SIGN_FLAG;
+        break;
+      case '#':
+        spec.flags_ |= HASH_FLAG;
+        break;
+      default:
+        --s;
+        return;
+    }
+  }
+}
+
+template <typename Char, typename AF>
+Arg PrintfFormatter<Char, AF>::get_arg(const Char *s, unsigned arg_index) {
+  (void)s;
+  const char *error = 0;
+  Arg arg = arg_index == std::numeric_limits<unsigned>::max() ?
+    next_arg(error) : FormatterBase::get_arg(arg_index - 1, error);
+  if (error)
+    FMT_THROW(FormatError(!*s ? "invalid format string" : error));
+  return arg;
+}
+
+template <typename Char, typename AF>
+unsigned PrintfFormatter<Char, AF>::parse_header(
+  const Char *&s, FormatSpec &spec) {
+  unsigned arg_index = std::numeric_limits<unsigned>::max();
+  Char c = *s;
+  if (c >= '0' && c <= '9') {
+    // Parse an argument index (if followed by '$') or a width possibly
+    // preceded with '0' flag(s).
+    unsigned value = parse_nonnegative_int(s);
+    if (*s == '$') {  // value is an argument index
+      ++s;
+      arg_index = value;
+    } else {
+      if (c == '0')
+        spec.fill_ = '0';
+      if (value != 0) {
+        // Nonzero value means that we parsed width and don't need to
+        // parse it or flags again, so return now.
+        spec.width_ = value;
+        return arg_index;
+      }
+    }
+  }
+  parse_flags(spec, s);
+  // Parse width.
+  if (*s >= '0' && *s <= '9') {
+    spec.width_ = parse_nonnegative_int(s);
+  } else if (*s == '*') {
+    ++s;
+    spec.width_ = WidthHandler(spec).visit(get_arg(s));
+  }
+  return arg_index;
+}
+
+template <typename Char, typename AF>
+void PrintfFormatter<Char, AF>::format(
+    BasicWriter<Char> &writer, BasicCStringRef<Char> format_str) {
+  const Char *start = format_str.c_str();
+  const Char *s = start;
+  while (*s) {
+    Char c = *s++;
+    if (c != '%') continue;
+    if (*s == c) {
+      write(writer, start, s);
+      start = ++s;
+      continue;
+    }
+    write(writer, start, s - 1);
+
+    FormatSpec spec;
+    spec.align_ = ALIGN_RIGHT;
+
+    // Parse argument index, flags and width.
+    unsigned arg_index = parse_header(s, spec);
+
+    // Parse precision.
+    if (*s == '.') {
+      ++s;
+      if ('0' <= *s && *s <= '9') {
+        spec.precision_ = static_cast<int>(parse_nonnegative_int(s));
+      } else if (*s == '*') {
+        ++s;
+        spec.precision_ = PrecisionHandler().visit(get_arg(s));
+      }
+    }
+
+    Arg arg = get_arg(s, arg_index);
+    if (spec.flag(HASH_FLAG) && IsZeroInt().visit(arg))
+      spec.flags_ &= ~to_unsigned<int>(HASH_FLAG);
+    if (spec.fill_ == '0') {
+      if (arg.type <= Arg::LAST_NUMERIC_TYPE)
+        spec.align_ = ALIGN_NUMERIC;
+      else
+        spec.fill_ = ' ';  // Ignore '0' flag for non-numeric types.
+    }
+
+    // Parse length and convert the argument to the required type.
+    switch (*s++) {
+    case 'h':
+      if (*s == 'h')
+        ArgConverter<signed char>(arg, *++s).visit(arg);
+      else
+        ArgConverter<short>(arg, *s).visit(arg);
+      break;
+    case 'l':
+      if (*s == 'l')
+        ArgConverter<fmt::LongLong>(arg, *++s).visit(arg);
+      else
+        ArgConverter<long>(arg, *s).visit(arg);
+      break;
+    case 'j':
+      ArgConverter<intmax_t>(arg, *s).visit(arg);
+      break;
+    case 'z':
+      ArgConverter<std::size_t>(arg, *s).visit(arg);
+      break;
+    case 't':
+      ArgConverter<std::ptrdiff_t>(arg, *s).visit(arg);
+      break;
+    case 'L':
+      // printf produces garbage when 'L' is omitted for long double, no
+      // need to do the same.
+      break;
+    default:
+      --s;
+      ArgConverter<void>(arg, *s).visit(arg);
+    }
+
+    // Parse type.
+    if (!*s)
+      FMT_THROW(FormatError("invalid format string"));
+    spec.type_ = static_cast<char>(*s++);
+    if (arg.type <= Arg::LAST_INTEGER_TYPE) {
+      // Normalize type.
+      switch (spec.type_) {
+      case 'i': case 'u':
+        spec.type_ = 'd';
+        break;
+      case 'c':
+        // TODO: handle wchar_t
+        CharConverter(arg).visit(arg);
+        break;
+      }
+    }
+
+    start = s;
+
+    // Format argument.
+    AF(writer, spec).visit(arg);
+  }
+  write(writer, start, s);
+}
+}  // namespace internal
+
+template <typename Char>
+void printf(BasicWriter<Char> &w, BasicCStringRef<Char> format, ArgList args) {
+  internal::PrintfFormatter<Char>(args).format(w, format);
+}
+
+/**
+  \rst
+  Formats arguments and returns the result as a string.
+
+  **Example**::
+
+    std::string message = fmt::sprintf("The answer is %d", 42);
+  \endrst
+*/
+inline std::string sprintf(CStringRef format, ArgList args) {
+  MemoryWriter w;
+  printf(w, format, args);
+  return w.str();
+}
+FMT_VARIADIC(std::string, sprintf, CStringRef)
+
+inline std::wstring sprintf(WCStringRef format, ArgList args) {
+  WMemoryWriter w;
+  printf(w, format, args);
+  return w.str();
+}
+FMT_VARIADIC_W(std::wstring, sprintf, WCStringRef)
+
+/**
+  \rst
+  Prints formatted data to the file *f*.
+
+  **Example**::
+
+    fmt::fprintf(stderr, "Don't %s!", "panic");
+  \endrst
+ */
+FMT_API int fprintf(std::FILE *f, CStringRef format, ArgList args);
+FMT_VARIADIC(int, fprintf, std::FILE *, CStringRef)
+
+/**
+  \rst
+  Prints formatted data to ``stdout``.
+
+  **Example**::
+
+    fmt::printf("Elapsed time: %.2f seconds", 1.23);
+  \endrst
+ */
+inline int printf(CStringRef format, ArgList args) {
+  return fprintf(stdout, format, args);
+}
+FMT_VARIADIC(int, printf, CStringRef)
+}  // namespace fmt
+
+#endif  // FMT_PRINTF_H_

test/CMakeLists.txt

@@ -80,6 +80,7 @@ add_fmt_test(printf-test)
 add_fmt_test(string-test)
 add_fmt_test(util-test mock-allocator.h)
 add_fmt_test(macro-test)
+add_fmt_test(custom-formatter-test)
 
 # Enable stricter options for one test to make sure that the header is free of
 # warnings.

test/custom-formatter-test.cc

@@ -0,0 +1,65 @@
+/*
+ Custom argument formatter tests
+
+ Copyright (c) 2016, Victor Zverovich
+ All rights reserved.
+
+ For the license information refer to format.h.
+ */
+
+#include "fmt/printf.h"
+#include "gtest-extra.h"
+
+using fmt::internal::BasicPrintfArgFormatter;
+
+// A custom argument formatter that doesn't print `-` for floating-point values
+// rounded to 0.
+class CustomArgFormatter
+  : public fmt::BasicArgFormatter<CustomArgFormatter, char> {
+ public:
+  CustomArgFormatter(fmt::BasicFormatter<char, CustomArgFormatter> &f,
+                     fmt::FormatSpec &s, const char *fmt)
+  : fmt::BasicArgFormatter<CustomArgFormatter, char>(f, s, fmt) {}
+
+  void visit_double(double value) {
+    if (round(value * pow(10, spec().precision())) == 0)
+      value = 0;
+    fmt::BasicArgFormatter<CustomArgFormatter, char>::visit_double(value);
+  }
+};
+
+// A custom argument formatter that doesn't print `-` for floating-point values
+// rounded to 0.
+class CustomPAF : public BasicPrintfArgFormatter<CustomPAF, char> {
+ public:
+  CustomPAF(fmt::BasicWriter<char> &writer, fmt::FormatSpec &spec)
+  : BasicPrintfArgFormatter<CustomPAF, char>(writer, spec) {}
+
+  void visit_double(double value) {
+    if (round(value * pow(10, spec().precision())) == 0)
+      value = 0;
+    BasicPrintfArgFormatter<CustomPAF, char>::visit_double(value);
+  }
+};
+
+std::string custom_format(const char *format_str, fmt::ArgList args) {
+  fmt::MemoryWriter writer;
+  // Pass custom argument formatter as a template arg to BasicFormatter.
+  fmt::BasicFormatter<char, CustomArgFormatter> formatter(args, writer);
+  formatter.format(format_str);
+  return writer.str();
+}
+FMT_VARIADIC(std::string, custom_format, const char *)
+
+std::string custom_sprintf(const char* fstr, fmt::ArgList args){
+  fmt::MemoryWriter writer;
+  fmt::internal::PrintfFormatter< char, CustomPAF > pfer( args);
+  pfer.format(writer, fstr);
+  return writer.str();
+}
+FMT_VARIADIC(std::string, custom_sprintf, const char*);
+
+TEST(CustomFormatterTest, Format) {
+  EXPECT_EQ("0.00", custom_format("{:.2f}", -.00001));
+  EXPECT_EQ("0.00", custom_sprintf("%.2f", -.00001));
+}

test/format-impl-test.cc

@@ -46,7 +46,7 @@ TEST(FormatTest, ArgConverter) {
   Arg arg = Arg();
   arg.type = Arg::LONG_LONG;
   arg.long_long_value = std::numeric_limits<fmt::LongLong>::max();
-  fmt::ArgConverter<fmt::LongLong>(arg, 'd').visit(arg);
+  fmt::internal::ArgConverter<fmt::LongLong>(arg, 'd').visit(arg);
   EXPECT_EQ(Arg::LONG_LONG, arg.type);
 }
 

test/printf-test.cc

@@ -29,6 +29,7 @@
 #include <climits>
 #include <cstring>
 
+#include "fmt/printf.h"
 #include "fmt/format.h"
 #include "gtest-extra.h"
 #include "util.h"