fmt/format.h

/*
 String formatting library for C++

 Copyright (c) 2012, Victor Zverovich
 All rights reserved.

 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:

 1. Redistributions of source code must retain the above copyright notice, this
    list of conditions and the following disclaimer.
 2. Redistributions in binary form must reproduce the above copyright notice,
    this list of conditions and the following disclaimer in the documentation
    and/or other materials provided with the distribution.

 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef FORMAT_H_
#define FORMAT_H_

#include <cstddef>
#include <cstdio>
#include <stdexcept>
#include <string>
#include <sstream>
#include <vector>

namespace format {

namespace internal {

// A simple array for POD types with the first SIZE elements stored in
// the object itself. It supports a subset of std::vector's operations.
template <typename T, std::size_t SIZE>
class Array {
 private:
  std::size_t size_;
  std::size_t capacity_;
  T *ptr_;
  T data_[SIZE];

  void Grow(std::size_t size);

  // Do not implement!
  Array(const Array &);
  void operator=(const Array &);

 public:
  Array() : size_(0), capacity_(SIZE), ptr_(data_) {}
  ~Array() {
    if (ptr_ != data_) delete [] ptr_;
  }

  // Returns the size of this array.
  std::size_t size() const { return size_; }

  // Returns the capacity of this array.
  std::size_t capacity() const { return capacity_; }

  // Resizes the array. If T is a POD type new elements are not initialized.
  void resize(std::size_t new_size) {
    if (new_size > capacity_)
      Grow(new_size);
    size_ = new_size;
  }

  void reserve(std::size_t capacity) {
    if (capacity > capacity_)
      Grow(capacity);
  }

  void clear() { size_ = 0; }

  void push_back(const T &value) {
    if (size_ == capacity_)
      Grow(size_ + 1);
    ptr_[size_++] = value;
  }

  // Appends data to the end of the array.
  void append(const T *begin, const T *end);

  T &operator[](std::size_t index) { return ptr_[index]; }
  const T &operator[](std::size_t index) const { return ptr_[index]; }
};

template <typename T, std::size_t SIZE>
void Array<T, SIZE>::Grow(std::size_t size) {
  capacity_ = std::max(size, capacity_ + capacity_ / 2);
  T *p = new T[capacity_];
  std::copy(ptr_, ptr_ + size_, p);
  if (ptr_ != data_)
    delete [] ptr_;
  ptr_ = p;
}

template <typename T, std::size_t SIZE>
void Array<T, SIZE>::append(const T *begin, const T *end) {
  std::ptrdiff_t num_elements = end - begin;
  if (size_ + num_elements > capacity_)
    Grow(num_elements);
  std::copy(begin, end, ptr_ + size_);
  size_ += num_elements;
}

class ArgInserter;
}

class FormatError : public std::runtime_error {
 public:
  explicit FormatError(const std::string &message)
  : std::runtime_error(message) {}
};

// Formatter provides string formatting functionality similar to Python's
// str.format. The output is stored in a memory buffer that grows dynamically.
// Usage:
//
//   Formatter out;
//   out("Current point:\n");
//   out("(-{:+f}, {:+f})") << 3.14 << -3.14;
//
// This will populate the buffer of the out object with the following output:
//
//   Current point:
//   (-3.140000, +3.140000)
//
// The buffer can be accessed using Formatter::data() or Formatter::c_str().
class Formatter {
 private:
  enum { INLINE_BUFFER_SIZE = 500 };
  internal::Array<char, INLINE_BUFFER_SIZE> buffer_;  // Output buffer.

  enum Type {
    // Numeric types should go first.
    INT, UINT, LONG, ULONG, DOUBLE, LONG_DOUBLE,
    LAST_NUMERIC_TYPE = LONG_DOUBLE,
    CHAR, STRING, WSTRING, POINTER, CUSTOM
  };

  typedef void (Formatter::*FormatFunc)(const void *arg, int width);

  // A format argument.
  class Arg {
   private:
    // This method is private to disallow formatting of arbitrary pointers.
    // If you want to output a pointer cast it to const void*. Do not implement!
    template <typename T>
    Arg(const T *value);

    // 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>
    Arg(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!
    Arg(wchar_t value);

   public:
    Type type;
    union {
      int int_value;
      unsigned uint_value;
      double double_value;
      long long_value;
      unsigned long ulong_value;
      long double long_double_value;
      const void *pointer_value;
      struct {
        const char *value;
        std::size_t size;
      } string;
      struct {
        const void *value;
        FormatFunc format;
      } custom;
    };
    mutable Formatter *formatter;

    Arg(int value) : type(INT), int_value(value), formatter(0) {}
    Arg(unsigned value) : type(UINT), uint_value(value), formatter(0) {}
    Arg(long value) : type(LONG), long_value(value), formatter(0) {}
    Arg(unsigned long value) : type(ULONG), ulong_value(value), formatter(0) {}
    Arg(double value) : type(DOUBLE), double_value(value), formatter(0) {}
    Arg(long double value)
    : type(LONG_DOUBLE), long_double_value(value), formatter(0) {}
    Arg(char value) : type(CHAR), int_value(value), formatter(0) {}

    Arg(const char *value) : type(STRING), formatter(0) {
      string.value = value;
      string.size = 0;
    }

    Arg(char *value) : type(STRING), formatter(0) {
      string.value = value;
      string.size = 0;
    }

    Arg(const void *value)
    : type(POINTER), pointer_value(value), formatter(0) {}

    Arg(void *value) : type(POINTER), pointer_value(value), formatter(0) {}

    Arg(const std::string &value) : type(STRING), formatter(0) {
      string.value = value.c_str();
      string.size = value.size();
    }

    template <typename T>
    Arg(const T &value) : type(CUSTOM), formatter(0) {
      custom.value = &value;
      custom.format = &Formatter::FormatCustomArg<T>;
    }

    ~Arg() {
      // Format is called here to make sure that a referred object is
      // still alive, for example:
      //
      //   Print("{0}") << std::string("test");
      //
      // Here an Arg object refers to a temporary std::string which is
      // destroyed at the end of the statement. Since the string object is
      // constructed before the Arg object, it will be destroyed after,
      // so it will be alive in the Arg's destructor where Format is called.
      // Note that the string object will not necessarily be alive when
      // the destructor of ArgInserter is called.
      formatter->Format();
    }
  };

  enum { NUM_INLINE_ARGS = 10 };
  internal::Array<const Arg*, NUM_INLINE_ARGS> args_;  // Format arguments.

  const char *format_;  // Format string.

  friend class internal::ArgInserter;

  void Add(const Arg &arg) {
    args_.push_back(&arg);
  }

  // Formats an integer.
  template <typename T>
  void FormatInt(T value, unsigned flags, int width, char type);

  // Formats a floating point number (double or long double).
  template <typename T>
  void FormatDouble(
      T value, unsigned flags, int width, int precision, char type);

  // Formats an argument of a custom type, such as a user-defined class.
  template <typename T>
  void FormatCustomArg(const void *arg, int width);

  void DoFormat();

  void Format() {
    if (!format_) return;
    DoFormat();
  }

  // Grows the buffer by n characters and returns a pointer to the newly
  // allocated area.
  char *GrowBuffer(std::size_t n) {
    std::size_t size = buffer_.size();
    buffer_.resize(size + n);
    return &buffer_[size];
  }

 public:
  Formatter() : format_(0) { buffer_[0] = 0; }

  // Formats a string appending the output to the internal buffer.
  // Arguments are accepted through the returned ArgInserter object
  // using inserter operator<<.
  internal::ArgInserter operator()(const char *format);

  std::size_t size() const { return buffer_.size(); }

  const char *data() const { return &buffer_[0]; }
  const char *c_str() const { return &buffer_[0]; }

  std::string str() const { return std::string(&buffer_[0], buffer_.size()); }
};

namespace internal {

// This is a transient object that normally exists only as a temporary
// returned by one of the formatting functions. It stores a reference
// to a formatter and provides operator<< that feeds arguments to the
// formatter.
class ArgInserter {
 private:
  mutable Formatter *formatter_;

  friend class format::Formatter;

 protected:
  explicit ArgInserter(Formatter *f = 0) : formatter_(f) {}

  ArgInserter(ArgInserter& other)
  : formatter_(other.formatter_) {
    other.formatter_ = 0;
  }

  ArgInserter& operator=(const ArgInserter& other) {
    formatter_ = other.formatter_;
    other.formatter_ = 0;
    return *this;
  }

  const Formatter *Format() const {
    Formatter *f = formatter_;
    if (f) {
      formatter_ = 0;
      f->Format();
    }
    return f;
  }

  Formatter *formatter() const { return formatter_; }
  const char *format() const { return formatter_->format_; }

  void ResetFormatter() { formatter_ = 0; }

 public:
  ~ArgInserter() {
    if (formatter_)
      formatter_->Format();
  }

  // Feeds an argument to a formatter.
  ArgInserter &operator<<(const Formatter::Arg &arg) {
    arg.formatter = formatter_;
    formatter_->Add(arg);
    return *this;
  }

  // Performs formatting and returns a C string with the output.
  friend const char *c_str(const ArgInserter &af) {
    return af.Format()->c_str();
  }

  // Performs formatting and returns a std::string with the output.
  friend std::string str(const ArgInserter &af) {
    return af.Format()->str();
  }
};
}

template <typename T>
void Formatter::FormatCustomArg(const void *arg, int width) {
  const T &value = *static_cast<const T*>(arg);
  std::ostringstream os;
  os << value;
  std::string str(os.str());
  char *out = GrowBuffer(std::max<std::size_t>(width, str.size()));
  std::copy(str.begin(), str.end(), out);
  if (static_cast<unsigned>(width) > str.size())
    std::fill_n(out + str.size(), width - str.size(), ' ');
}

inline internal::ArgInserter Formatter::operator()(const char *format) {
  internal::ArgInserter formatter(this);
  format_ = format;
  args_.clear();
  return formatter;
}

// A formatter with an action performed when formatting is complete.
// This is a transient object that normally exists only as a temporary
// returned by one of the formatting functions.
template <typename Action>
class ActiveFormatter : public internal::ArgInserter {
 private:
  Formatter formatter_;
  Action action_;

  // Do not implement.
  ActiveFormatter& operator=(const ActiveFormatter&);

 public:
  // Creates an active formatter with a format string and an action.
  // Action should be an unary function object that takes a const
  // reference to Formatter as an argument. See Ignore and Write
  // for examples of action classes.
  explicit ActiveFormatter(const char *format, Action a = Action())
  : action_(a) {
    ArgInserter::operator=(formatter_(format));
  }

  // Creates an active formatter with the same format string and action
  // as other has and modifies other so that it doesn't call action in
  // destructor. Note that the buffer content is not copied because the
  // the buffer in ActiveFormatter is populated when all the arguments
  // are provided.
  ActiveFormatter(ActiveFormatter &other)
  : ArgInserter(0), action_(other.action_) {
    ArgInserter::operator=(formatter_(other.format()));
    other.ResetFormatter();
  }

  ~ActiveFormatter() {
    if (formatter())
      action_(*Format());
  }
};

// A formatting action that does nothing.
struct Ignore {
  void operator()(const Formatter &) const {}
};

// Formats a string.
// Example:
//   std::string s = str(Format("Elapsed time: {0:.2f} seconds") << 1.23);
inline ActiveFormatter<Ignore> Format(const char *format) {
  ActiveFormatter<Ignore> af(format);
  return af;
}

// A formatting action that writes formatted output to stdout.
struct Write {
  void operator()(const Formatter &f) const {
    std::fwrite(f.data(), 1, f.size(), stdout);
  }
};

// Formats a string and prints it to stdout.
// Example:
//   Print("Elapsed time: {0:.2f} seconds") << 1.23;
inline ActiveFormatter<Write> Print(const char *format) {
  ActiveFormatter<Write> af(format);
  return af;
}
}

namespace fmt = format;

#endif  // FORMAT_H_