قراءة الملفات باستخدام ifstream

ما هو ifstream؟

#include <iostream>
#include <fstream>

int main() {
    std::ofstream("demo.txt") << "hello\n";
    std::ifstream in("demo.txt");
    std::string word;
    in >> word;
    std::cout << word << '\n';
    return 0;
}

فتح ملف

#include <iostream>
#include <fstream>

int main() {
    std::ofstream("data.txt") << "42\n";
    std::ifstream in("data.txt");
    std::cout << (in.is_open() ? "opened" : "failed") << '\n';
    return 0;
}

قراءة الكلمات

#include <iostream>
#include <fstream>

int main() {
    std::ofstream("words.txt") << "alpha beta gamma\n";
    std::ifstream in("words.txt");
    std::string w;
    while (in >> w) std::cout << w << '\n';
    return 0;
}

قراءة الأعداد

#include <iostream>
#include <fstream>

int main() {
    std::ofstream("nums.txt") << "10 20 30\n";
    std::ifstream in("nums.txt");
    int sum = 0, x;
    while (in >> x) sum += x;
    std::cout << "sum = " << sum << '\n';
    return 0;
}

قراءة الأسطر باستخدام getline

#include <iostream>
#include <fstream>
#include <string>

int main() {
    std::ofstream("lines.txt") << "first line\nsecond line\n";
    std::ifstream in("lines.txt");
    std::string line;
    while (std::getline(in, line)) std::cout << "[" << line << "]\n";
    return 0;
}

قراءة الملف بأكمله

#include <iostream>
#include <fstream>
#include <sstream>

int main() {
    std::ofstream("all.txt") << "line1\nline2\n";
    std::ifstream in("all.txt");
    std::stringstream ss;
    ss << in.rdbuf();
    std::cout << ss.str();
    return 0;
}

اكتشاف نهاية الملف

#include <iostream>
#include <fstream>

int main() {
    std::ofstream("eof.txt") << "1 2 3\n";
    std::ifstream in("eof.txt");
    int x, count = 0;
    while (in >> x) ++count;
    std::cout << "read " << count << " numbers\n";
    std::cout << "eof: " << std::boolalpha << in.eof() << '\n';
    return 0;
}

التعامل مع ملف مفقود

#include <iostream>
#include <fstream>

int main() {
    std::ifstream in("does_not_exist_12345.txt");
    if (!in) {
        std::cout << "could not open file\n";
    }
    return 0;
}

تحليل الأسطر المنظَّمة

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>

int main() {
    std::ofstream("people.txt") << "Alice 30\nBob 25\n";
    std::ifstream in("people.txt");
    std::string line;
    while (std::getline(in, line)) {
        std::istringstream ss(line);
        std::string name; int age;
        ss >> name >> age;
        std::cout << name << " is " << age << '\n';
    }
    return 0;
}

الفتح والإغلاق الصريحان

#include <iostream>
#include <fstream>

int main() {
    std::ofstream("oc.txt") << "data\n";
    std::ifstream in;
    in.open("oc.txt");
    std::string s; in >> s;
    in.close();
    std::cout << s << '\n';
    return 0;
}

يتولى RAII الإغلاق عنكم

#include <iostream>
#include <fstream>

int main() {
    std::ofstream("raii.txt") << "x\n";
    {
        std::ifstream in("raii.txt");
        std::string s; in >> s;
        std::cout << s << '\n';
    } // file closed here automatically
    std::cout << "closed\n";
    return 0;
}

اختبار سريع

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