如何在 C++ 中读取不断增长的文本文件?

2021-12-19 00:00:00 logging c++ stl fstream seekg

我正在尝试从一个正在增长的文件中读取数据(类似于 tail -F 所做的)，但我的代码肯定存在一些问题:

I am trying to read from a file which is growing (something similar to what tail -F does), but there must be some problems with my code:

string   log, logFile("test.log");
size_t   p = 0;

while(true)
{
    ifstream ifs(logFile.c_str());

    ifs.seekg(p);  //*1

    while(ifs.eof() == false)
    {
        getline(ifs, log);

        cout << log << endl;

        p = ifs.tellg();  //*2
    }

    nanosleep(&pause, NULL);
}

如果没有//*1 和//*2 行，日志文件会被正确读取到其末尾，但如果添加新行，则不会发生任何事情.

Without the lines //*1 and //*2, the log file is correctly read up to its end, but if new lines are added nothing happens.

使用 seekg 和 tellg，我试图存储文件的当前结束位置，这样当我重新打开它时，我就可以直接去那里阅读已添加的内容.

With seekg and tellg I am trying to store the current end position of the file, so that when I reopen it I can go strait there and read what has been added.

我想知道我的代码有什么问题，以及是否真的有必要为此目的关闭并重新打开同一个文件.

I would like to know what is wrong in my code, and if it is really necessary to close and reopen the same file for this purpose.

谢谢.

推荐答案

由于这些答案都不起作用，我想出了一个可行的方法...

Since none of these answers worked, i came up with one that does work...

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

using namespace std;

int main()
{
    string   log, logFile("test.txt");
    std::streamoff   p = 0;
    ifstream ifs(logFile.c_str());

    while(true)
    {

        ifs.seekg(p);  //*1
        while (getline(ifs, log))
        {
            cout << log << endl;
            if(ifs.tellg() == -1) p = p + log.size();
            else p = ifs.tellg();
        }
        ifs.clear();

    }
}

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