# C++ 讀檔&寫檔筆記
宣告fstream
**每次寫完絕對要記得關檔( f.close() )**
## 寫檔(ofstream)

ofstream outputFile; 
string s; 
outputFile.open("Friends.txt",ios::app); 
cin >> s;
outputFile << s << endl;
outputFile.close(); 

寫檔時也可使用iomanip的各種做法，如

outputFile << showpoint << fixed << setprecision(2);

## 讀檔(ifstream)

ifstream inputFile;
string s;
inputFile.open("Friends.txt");
if (inputFile){
    while(inputFile >> s) 
        cout << s << endl;
    inputFile.close();
}

也可以用getline方式讀整行

string s;
getline(inputFile, s);

## 可寫也可讀(fstream)
可在open的第二個參數控制權限

#include<fstream>

fstream inOutFile; 
string word; 

inOutFile.open("inout.txt"); 
if (inOutFIle.fail()) {
    cout << "The file was not found." << endl; 
	return 1; 
} 

// Read and print every word already in the file 
while (inOutFile >> word) 
    cout << word << endl; 

// Clear end of file flag to allow additional file operations 
inOutFile.clear(); 

// Write a word to the file and close the file 
inOutFile << "Hello" << endl; 
inOutFile.close(); 

## open函式

ofstream outputFile;
outputFile.open(檔名,模式)

### 第一個參數
第一個參數為檔名，若無此檔則會新開一個
可以直接打，也可以用輸入檔名的方式用變數傳入，但要注意，只能用C的字元串，不可用C++的string，需用stringObject.c_str()

ifstream inputFile;
string filename;
inputFile.open(filename.c_str());

### 第二個參數
第二個參數決定要覆寫、從後面加或是單純讀取。
* ios::out ：**預設設置**，覆寫
* ios::app ：從檔案最後加入
* ios::in : 單純讀取
* ios::out : 單純寫檔
* ios::trunc : file contents are discarded
## Error State Bits
* ios::eofbit : set when end of file detected
* ios::failbit : set when operation failed
* ios::hardfail set when an irrecoverable error occurred
* ios::badbit set when invalid operation attempted
* ios::goodbit set when no other bits are set
* eof() true if eofbit set, false otherwise
* fail() true if failbit or hardfail set, false otherwise
* bad() true if badbit set, false otherwise
* good() true if goodbit set, false otherwise
* clear() clear all flags (no arguments), or clear a specific flag

void showState(fstream &file){
    cout << "File Status:\n";
    cout << " eof bit: " << file.eof() << endl;
    cout << " fail bit: " << file.fail() << endl;
    cout << " bad bit: " << file.bad() << endl;
    cout << " good bit: " << file.good() << endl;
    file.clear(); // Clear any bad bits.
}

## 輸入(讀檔)方法
### getline
getline(字串流，傳入的字串，讀取結束的符號，若未寫則默認為\n)

string input;
fstream dataFile("addresses.txt", ios::in);
getline(dataFile, input, '$');

## get
讀入單一字元，不會忽略任何符號，讀入後指標向下一位置移動

//the content of file: abc
char ch = inFile.get(); 
cout << ch; 
ch = inFile.get(); 
cout << ch; 

輸出 ：ab

## peek
讀入單一字元，不會忽略任何符號，讀入後指標**不移動**

//the content of file: abc
char ch = inFile.peek(); 
cout << ch; 
ch = inFile.get();
cout << ch; 

輸出 ：aa

## seekg
seekg(offset, place);
seekp用於打開要進行輸出的文件，而 seekg 則適用於打開用於輸入的文件

## Binary file

file.open("stuff.dat", ios::out | ios::binary);
write(char *addressOfBuffer, int numberOfBytes);

double dl = 45.9;
double dArray[3] = { 12.3, 45.8, 19.0 };
ofstream outFile("stuff.dat", ios::binary);
outFile.write(reinterpret_cast<char *>(&dl), sizeof(d1));
outFile.write(reinterpret_cast<char *>(dArray),sizeOf(dArray));

char ch = 'X';
char charArray[5] = "Hello";
outFile.write(&ch, sizeof(ch));
outFile.write(charArray, sizeof(charArray));