目錄

標頭檔案 <fstream>包含的多個檔案流類，這裡列出常用的4個：

• ifstream Input file stream class (class )連結
• ofstream Output file stream (class )連結
• fstream Input/output file stream class (class )連結
• filebuf File stream buffer (class )連結

輸入流的繼承關係：

ios_base <- ios <- ostream <- ofstream

Public member functions (1-6)

1， (constructor)

default (1) ofstream(); // 只定義不關聯

initialization (2)  //關聯檔案filename，預設模式 ios_base::out
explicit ofstream (const char* filename, ios_base::openmode mode = ios_base::out);
explicit ofstream (const string& filename, ios_base::openmode mode = ios_base::out);

copy (3)    //禁止拷貝賦值
ofstream (const
 
 ofstream&) = delete;

move (4)    //可以右值引用臨時變數賦值
ofstream (ofstream&& x);

2， ofstream::open

//和第二種建構函式一樣，繫結檔案
void open (const   char* filename,  ios_base::openmode mode = ios_base::out);
void open (const string& filename,  ios_base::openmode mode = ios_base::out);

3， ofstream::is_open

bool is_open() const;
// 檔案開啟返回 true ，否則 false

4， ofstream::close

void close();
// Closes the file currently associated with the object, disassociating it from the stream.

5， ofstream::rdbuf

filebuf* rdbuf() const;
// 返回一個指標，指向 filebuf 物件，filebuf 要麼通過open()和檔案繫結，要麼通過rdbuf（）與fstream物件繫結，繫結後才能使用。

int main () {
  std::ifstream ifs ("test.txt");
  std::ofstream ofs ("copy.txt");

  std::filebuf* inbuf  = ifs.rdbuf();
  std::filebuf* outbuf = ofs.rdbuf();

  char c = inbuf->sbumpc();
  while (c != EOF)
  {
    outbuf->sputc (c);
    c = inbuf->sbumpc();
  }
  ofs.close();
  ifs.close();
  return 0;
}

6，ofstream::operator=

copy (1) //禁止copy賦值
ofstream& operator= (const ofstream&) = delete;
move (2） // 可以右值引用建立物件。
ofstream& operator= (ofstream&& rhs);

Public member functions inherited from ostream (7-11)

7，std::ostream::operator<<

用法和 cout<< 一樣，是寫資料到檔案最方便的函式，過載了常用的資料型別。

 arithmetic types (1)   
ostream& operator<< (bool val);
ostream& operator<< (short val);
ostream& operator<< (unsigned short val);
ostream& operator<< (int val);
ostream& operator<< (unsigned int val);
ostream& operator<< (long val);
ostream& operator<< (unsigned long val);
ostream& operator<< (long long val);
ostream& operator<< (unsigned long long val);
ostream& operator<< (float val);
ostream& operator<< (double val);
ostream& operator<< (long double val);
ostream& operator<< (void* val);

stream buffers (2)  
ostream& operator<< (streambuf* sb );

manipulators (3)    
ostream& operator<< (ostream& (*pf)(ostream&));
ostream& operator<< (ios& (*pf)(ios&));
ostream& operator<< (ios_base& (*pf)(ios_base&));

用string資料型別，作為引數寫入到ofstream，在標頭檔案<string>
中對輸出運算子過載。
std::operator<< (string)

ostream& operator<< (ostream& os, const string& str);

8，ostream::put

ostream& put (char c);
//插入字元 c 到流中

9，ostream::write

ostream& write (const char* s, streamsize n);
//從陣列s中取n 個字元插入到流中

10，ostream::tellp

streampos tellp();
返回檔案指標的位置， streampos 可以轉為int

11，ostream::seekp

(1) 
ostream& seekp (streampos pos);
(2) 
ostream& seekp (streamoff off, ios_base::seekdir way);

//Sets the position where the next character is to be inserted into the output stream.

引數 pos 是流中的絕對位置可以轉化為 int
引數 off 是偏移量，與way相關，型別是 int
引數 way 可以選下表中的任意一個常量。

Public member functions inherited from ios(12-14)

12，ios::good

bool good() const;
bool eof() const;
bool fail() const;
bool bad() const;

檢測流的狀態是否正常。當錯誤的狀態flags (eofbit, failbit and badbit) 都沒被設定的時候返回true
特定的錯誤狀態可以用下面的函式（eof, fail, and bad）來檢測。

13，ios::operator!

bool operator!() const;
//Returns true if either failbit or badbit is set, and false otherwise.
// 有錯誤狀態返回 true

// evaluating a stream (not)
#include <iostream>     // std::cout
#include <fstream>      // std::ifstream

int main () {
  std::ifstream is;
  is.open ("test.txt");
  if (!is)
    std::cerr << "Error opening 'test.txt'\n";
  return 0;
}

14，ios::operator bool

explicit operator bool() const;
C++11: Return true if none of failbit or badbit is set. false otherwise.
// 在條件語句中，無錯誤返回真，有錯返回假。
int main () {
  std::ifstream is;
  is.open ("test.txt");
  if (is) {
    // read file
  }
  else {
    std::cerr << "Error opening 'test.txt'\n";
  }
  return 0;
}