🗂️前言

📄ref

• std::basic_fstream - cppreference.com
• std::basic_ifstream - cppreference.com
• std::basic_ofstream - cppreference.com

📄访问标记

🗃️流打开模式类型

std::ios_base::openmode - cppreference.com

常量	描述
app	每次写入前寻位到流结尾
binary	以二进制模式打开
in	为读打开
out	为写打开
trunc	在打开时舍弃流的内容
ate	打开后立即寻位到流结尾
noreplace (C++23)	以独占模式打开

🗂️Code

📄demo

#include <cstring>
#include <fstream>
#include <iostream>void check_io(std::ios& io) {if (io.good()) {std::cerr << " io is good." << std::endl;}if (io.fail()) {std::cerr << " io is fail." << std::endl;}if (io.bad()) {std::cerr << " io is bad." << std::endl;}if (io.eof()) {std::cerr << " io is eof." << std::endl;}io.clear();
}void file_write(std::string file_path) {std::ofstream ofs;ofs.open(file_path, std::ios::out);if (!ofs.is_open()) {std::cerr << "File Open Error" << std::endl;return;}char msg[] = "https://space.bilibili.com/8172252";ofs << "cuber-lotus" << std::endl;for (char ch : {'u', 'r', 'l', ':'}) {ofs.put(ch);}ofs.write(msg, strlen(msg));std::cout << __func__;check_io(ofs);ofs.close();
}void file_read(std::string file_path) {std::ifstream ifs;ifs.open(file_path, std::ios::in);if (!ifs.is_open()) {std::cerr << "File Open Error" << std::endl;return;}#define CASE 1#if CASE == 1char buf[1024] = {};while (ifs >> buf) {std::cout << buf << std::endl;}
#elif CASE == 2char buf[1024] = {};while (ifs.getline(buf, sizeof(buf))) {std::cout << buf << std::endl;}
#elif CASE == 3std::string buf;while (std::getline(ifs, buf)) {std::cout << buf << std::endl;}
#elif CASE == 4int ch;while ((ch = ifs.get()) != EOF) {std::cout << (char)ch;}std::cout << std::endl;
#elif CASE == 5char buf[1024] = {};while (ifs.read(buf, sizeof(buf))) {std::cout << buf << std::endl;}
#endifstd::cout << __func__;check_io(ifs);ifs.close();
}int main() {const std::string file_path = "example.txt";file_write(file_path);file_read(file_path);
}

📄分点讲解

C++用类封装了流式操作，使用体验是更加丰富，更加多。

🗃️打开/关闭

// fstream 可以同时管理 i/o
std::fstream fs;
fs.open(file_path, std::ios::out | std::ios::in);
if (!fs.is_open()) {std::cerr << "File Open Error" << std::endl;return;
}
fs.close();

🗃️写

法1：

ofs << "cuber-lotus" << std::endl;

法2：

char msg[] = "https://space.bilibili.com/8172252";
ofs.write(msg, strlen(msg));

法3：

ofs.put(ch);

🗃️读

法1：

char buf[1024] = {};
while (ifs >> buf) {std::cout << buf << std::endl;
}

法2：

char buf[1024] = {};
while (ifs.getline(buf, sizeof(buf))) {std::cout << buf << std::endl;
}

法3：

std::string buf;
while (std::getline(ifs, buf)) {std::cout << buf << std::endl;
}

法4：

int ch;
while ((ch = ifs.get()) != EOF) {std::cout << (char)ch;
}
std::cout << std::endl;

法5：

char buf[1024] = {};
while (ifs.read(buf, sizeof(buf))) {std::cout << buf << std::endl;
}

🗃️状态函数

状态函数
good	检查是否没有发生错误，即是否可执行输入/输出操作 (std::basic_ios<CharT,Traits> 的公开成员函数)
eof	检查是否到达了文件末尾 (std::basic_ios<CharT,Traits> 的公开成员函数)
fail	检查是否发生了可恢复的错误 (std::basic_ios<CharT,Traits> 的公开成员函数)
bad	检查是否已发生不可恢复的错误 (std::basic_ios<CharT,Traits> 的公开成员函数)
operator!	检查是否有错误发生（fail() 的同义词） (std::basic_ios<CharT,Traits> 的公开成员函数)
operator bool	检查是否没有发生错误（!fail() 的同义词） (std::basic_ios<CharT,Traits> 的公开成员函数)
rdstate	返回状态标志 (std::basic_ios<CharT,Traits> 的公开成员函数)
setstate	设置状态标志 (std::basic_ios<CharT,Traits> 的公开成员函数)
clear	修改状态标志 (std::basic_ios<CharT,Traits> 的公开成员函数)

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🗂️END

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