C++ fstream 類

示例

使用 fstream 讀寫檔案

#include <iostream>
#include <fstream>
using namespace std;

int main() {
  // Create and open a text file
  fstream MyFile("filename.txt");

  // Write to the file
  MyFile << "Files can be tricky, but it is fun enough!";
  
  // Read from the file
  string myText;
  getline(MyFile, myText);
  cout << myText;

  // Close the file
  MyFile.close();
} 

fstream MyFile("filename.txt");

MyFile.seekg(6)

將讀檔案指標移動到不同位置

MyFile.seekg(6, fstream::beg);
cout << MyFile.tellg() << "\n";
MyFile.seekg(-3, fstream::cur);
cout << MyFile.tellg() << "\n";
MyFile.seekg(-4, fstream::end);
cout << MyFile.tellg() << "\n";

cout << MyFile.tellg();

MyFile.seekp(6)

將寫檔案指標移動到不同位置

MyFile.seekp(6, fstream::beg);
cout << MyFile.tellp() << "\n";
MyFile.seekp(-3, fstream::cur);
cout << MyFile.tellp() << "\n";
MyFile.seekp(-4, fstream::end);
cout << MyFile.tellp() << "\n";

cout << MyFile.tellp();

char myChar = MyFile.get();
cout << myChar;

char destination[20];
MyFile.get(destination, 20);
cout << destination << "\n";

// Stop reading when a '.' is found
MyFile.get(destination, 20, '.');
cout << destination << "\n";

char destination[20];
MyFile.getline(destination, 20);
cout << destination << "\n";

// Stop reading when a '.' is found
MyFile.getline(destination, 20, '.');
cout << destination << "\n";

string destination;
getline(MyFile, destination);
cout << destination << "\n";

// Stop reading when a '.' is found
getline(MyFile, destination, '.');
cout << destination << "\n";

char destination[20];
MyFile.read(destination, 19);
destination[20] = '\0'; // Make sure it ends with a null terminating character
cout << destination << "\n";

char myChar = MyFile.peek();
cout << myChar;

char destination[20];
MyFile.getline(destination, 20);
cout << MyFile.gcount() << "\n";

char myStr[] = "Hello World!";
MyFile.write(myStr, 5);

char grade = 'B';
MyFile.put(grade);

ofstream MyFile;
MyFile.open("filename.txt");

fstream MyFile;
cout << MyFile.is_open(); << "\n"; // Displays 0 because the file is not open
MyFile.open("filename.txt");
cout << MyFile.is_open(); << "\n"; // Displays 1 because the file is open

MyFile.close();

filebuf * buf = MyFile.rdbuf();

語法

MyFile >> variable

MyFile >> variable1 >> variable2 >> variable3

示例

使用運算子改變資料的解釋方式

bool myBool;
int myInt;

// Interpret character sequences "true" and "false" as boolean values
MyFile >> boolalpha >> myBool;

// Revert to reading booleans normally
MyFile >> noboolalpha;

// Read hexadecimal numbers from the file and interpret them as integers
MyFile >> hex >> myInt;

// Revert to reading integers normally
MyFile >> dec;

int year = 2024;
MyFile << year << "\n";
MyFile << "Files can be tricky, but it is fun enough!";