如何在文本文件C ++中查找和替换一行数据 [英] How can I find and replace a line of data in a text file c++

问题描述

我试图在c ++中的文本文件中查找并替换一行数据.但老实说，我不知道从哪里开始.

I am trying to find and replace a line of data in a text file in c++. But I honestly have no idea where to start.

我正在考虑使用 replaceNumber.open("test.txt"，ios :: in | ios :: out | ios_base :: beg | ios :: app);

I was thinking of using replaceNumber.open("test.txt", ios::in | ios::out | ios_base::beg | ios::app);

要从头开始打开文件并追加到文件上，但这是行不通的.

To open the file at the beginning and append over it but this doesn't work.

有人知道实现此任务的方法吗?

Does anyone know of a way to achieve this task?

谢谢

我的文本文件只有一行，并且包含一个数字，例如504.然后，用户指定一个要减去的数字，然后结果应替换文本文件中的原始数字.

My text file is only one line and it contains a number for example 504. The user then specifies a number to subtract then the result of that should replace the original number in the text file.

推荐答案

是的，您可以使用std :: fstream做到这一点，这是一个快速的实现，我很快就提出了.您打开文件，遍历文件中的每一行，并替换子字符串的所有出现.替换子字符串后，将行存储到字符串向量中，关闭文件，用std::ios::trunc重新打开，然后将每一行写回到空文件中.

Yes, you can do this using std::fstream, here's a quick implementation i whipped up real quick. You open the file, iterate over each line in the file, and replace any occurrences of your substring. After replacing the substring, store the line into a vector of strings, close the file, reopen it with std::ios::trunc, and write each line back to the empty file.

std::fstream file("test.txt", std::ios::in);

if(file.is_open()) {
    std::string replace = "bar";
    std::string replace_with = "foo";
    std::string line;
    std::vector<std::string> lines;

    while(std::getline(file, line)) {
        std::cout << line << std::endl;

        std::string::size_type pos = 0;

        while ((pos = line.find(replace, pos)) != std::string::npos){
            line.replace(pos, line.size(), replace_with);
            pos += replace_with.size();
        }

        lines.push_back(line);
    }

    file.close();
    file.open("test.txt", std::ios::out | std::ios::trunc);

    for(const auto& i : lines) {
        file << i << std::endl;
    }
}

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