文件流类

ifstream(读操作)
ofstream(写操作)
fstream(读写操作)

写文件

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#include<fstream>
ofstream ofs;
ofs.open("文件路径",打开方式);
ofs<<"...";
ofs.close();
打开方式 解释
ios::in 为读文件打开
ios:out 为写文件打开
ios::ate 初始位置在文件尾
ios:app 追加方式写文件
ios:trunc 如果文件存在先删除，再创建
ios::binary 二进制方式

读文件

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#include<fstream>
ifstream ifs;
ifs.open("文件路径",打开方式);
char buffer[1024];
while(ifs.read(buffer, sizeof(buffer) - 1)){
    buffer[ifs.gcount()]='\0';
    cout<<buffer;
    memset(buffer, 0, sizeof(buffer));
}
ifs.close();

检索文件

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#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;

vector<string> findSentencesWithKeyword(const string& filename, const string& keyword) {
    vector<string> sentences;
    ifstream infile(filename); 
    if (!infile) {
        cerr << "无法打开文件: " << filename << endl;
        return sentences;
    }

    string line;
    while (getline(infile, line)) { 
        istringstream iss(line); 
        string sentence;
        while (getline(iss, sentence, '.')) { // 按句号分割句子
            if (sentence.find(keyword) != string::npos) { 
                sentences.push_back(sentence + "."); 
            }
        }
    }

    infile.close(); 
    return sentences;
}

int main() {
    string filename;
    cout << "请输入文件名: ";
    cin >> filename;

    string keyword;
    cout << "请输入关键词: ";
    cin >> keyword;

    vector<string> sentences = findSentencesWithKeyword(filename, keyword); 

    if (sentences.empty()) {
        cout << "未找到包含关键词的句子。" << endl;
        return 0;
    }

    cout << "按回车键显示下一个包含关键词的句子，输入 'q' 退出。" << endl;
    char input;
    for (size_t i = 0; i < sentences.size(); ++i) {
        cin.get(input); // 等待用户输入
        if (input == 'q') {
            break;
        }
        cout << "找到句子: " << sentences[i] << endl;
    }

    return 0;
}