(C++) 文件读写基础

🗂️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

🗂️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 == 1
    char buf[1024] = {};
    while (ifs >> buf) {
        std::cout << buf << std::endl;
    }
#elif CASE == 2
    char buf[1024] = {};
    while (ifs.getline(buf, sizeof(buf))) {
        std::cout << buf << std::endl;
    }
#elif CASE == 3
    std::string buf;
    while (std::getline(ifs, buf)) {
        std::cout << buf << std::endl;
    }
#elif CASE == 4
    int ch;
    while ((ch = ifs.get()) != EOF) {
        std::cout << (char)ch;
    }
    std::cout << std::endl;
#elif CASE == 5
    char buf[1024] = {};
    while (ifs.read(buf, sizeof(buf))) {
        std::cout << buf << std::endl;
    }
#endif

    std::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

🗂️END

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