getline返回同一行的倍数

std::getline is returning multiples of the same line

本文关键字：一行 返回 getline      更新时间：2023-10-16

我正在解析一个.txt文件，以便制作一个Exp计算器，我得到一个奇怪的错误，它将加倍任何行，从流中有多行。我使用这段代码来打开和关闭文件以检查更改，并且只打印更改。

这是文本文件的样子..

[11:58:18] Mind increased by 0.000013 to 28.160389
[11:58:18] Mind logic increased by 0.000015 to 33.213428
[11:58:18] Miscellaneous items increased by 0.000061 to 59.381138
[11:58:18] Repairing increased by 0.000782 to 35.52212
[11:58:19] Mind increased by 0.000015 to 28.160404

当我添加Sleep来减慢它的速度时，它确实逐个获取每行并将它们打印到控制台，但在它完成后，它继续打印流中有1行以上的每行。

#include <windows.h>
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
int main()
{
    ios::streampos file_end;
    ifstream file ("C://Users//Matthew//wurm//players//Maximillian//logs//_Skills.2013-03.txt");
    if(file.is_open())
    {
        file.seekg( ios::beg, ios::end );
        file_end = file.tellg();
        file.close();
    }else{
        cout << "Unable to open file";
    }
    while(true)
    {
        ifstream file ("C://Users//Matthew//wurm//players//Maximillian//logs//_Skills.2013-03.txt");
        if (file.is_open())
        {
            file.seekg( ios::beg, ios::end );
            streampos new_end = file.tellg();
            if(new_end > file_end)
            {
                file.seekg(file_end);
                string line;
                while(getline(file, line))
                {
                    if(!line.empty())
                        cout << line << endl;
                    Sleep(1000);
                }
                file_end = new_end;
            }
            file.close();
        }else{
            cout << "Unable to open file";
        }
    }
    return 0;
}

这是输出…注意时间戳。我不知道它为什么会这样…

[16:42:36] Mind logic increased by 0.000015 to 33.349262
[16:42:36] Miscellaneous items increased by 0.000053 to 59.777897
[16:42:36] Repairing increased by 0.000694 to 36.59152
[16:42:37] Mind increased by 0.000013 to 28.270370
[16:42:37] Mind logic increased by 0.000019 to 33.349281
[16:42:38] Mind increased by 0.000013 to 28.270384
[16:42:38] Mind logic increased by 0.000015 to 33.349297
[16:42:38] Repairing increased by 0.000694 to 36.59222
[16:42:39] Mind logic increased by 0.000015 to 33.349312
[16:42:40] Repairing increased by 0.000694 to 36.59291
[16:42:42] Mind increased by 0.000015 to 28.270399
[16:42:42] Mind logic increased by 0.000015 to 33.349327
[16:42:42] Repairing increased by 0.000694 to 36.59361
[16:42:43] Mind increased by 0.000013 to 28.270412
[16:42:43] Mind logic increased by 0.000015 to 33.349342
[16:42:44] Mind increased by 0.000013 to 28.270426
[16:42:44] Mind logic increased by 0.000019 to 33.349361
[16:42:44] Repairing increased by 0.000694 to 36.59430
//I added this afterwards to break up what I printed out first... why did it reprint all the times that had 2 or more lines at once?
[16:42:36] Miscellaneous items increased by 0.000053 to 59.777897
[16:42:36] Repairing increased by 0.000694 to 36.59152
[16:42:37] Mind increased by 0.000013 to 28.270370
[16:42:37] Mind logic increased by 0.000019 to 33.349281
[16:42:38] Mind increased by 0.000013 to 28.270384
[16:42:38] Mind logic increased by 0.000015 to 33.349297
[16:42:38] Repairing increased by 0.000694 to 36.59222
[16:42:39] Mind logic increased by 0.000015 to 33.349312
[16:42:40] Repairing increased by 0.000694 to 36.59291
[16:42:42] Mind increased by 0.000015 to 28.270399
[16:42:42] Mind logic increased by 0.000015 to 33.349327
[16:42:42] Repairing increased by 0.000694 to 36.59361
[16:42:43] Mind increased by 0.000013 to 28.270412
[16:42:43] Mind logic increased by 0.000015 to 33.349342
[16:42:44] Mind increased by 0.000013 to 28.270426
[16:42:44] Mind logic increased by 0.000019 to 33.349361
[16:42:44] Repairing increased by 0.000694 to 36.59430

在getline() -循环之后，流中的读位置不能保证等于new_end，因为有人可能在您确定new_end之后写入文件，但在您读取它之前或期间。

这将导致打印一些行，然后将file_end调整为表明尚未打印这些行的值。这些行将在外部while -循环的下一次迭代中第二次打印。

通过再次调用tellg()来更新file_end，而不是通过从new_end赋值。你必须在做更新之前调用流上的clear()，因为std::getline()被调用直到流上的failbit被设置，这导致tellg()返回-1(即不是文件结束的实际位置)。

解决方案是在更新之前清除()tellg()函数，并且我还以不同的方式更新file_end和new_end。

while(true)
{
    ifstream file ("C://Users//Matthew//wurm//players//Maximillian//logs//_Skills.2013-03.txt");
    if (file.is_open())
    {
        if(new_end > file_end)
        {
            file.seekg(file_end);
            string line, output;
            while(getline(file, line))
            {
                //if(!line.empty())
                //    cout << line << endl;
                int f1 = line.find("] ")+2;
                int f2 = line.find(" increased ");
                if(f1 != line.string::npos && f2 != string::npos)
                {
                    output.append(line, f1, (f2-f1));
                    output += " ";
                    f1 = line.find(" by ") + 4;
                    f2 = line.find(" to ");
                    if(f1 != string::npos && f2 != string::npos)
                    {
                        output.append(line, f1, (f2-f1));
                        output += " ";
                    }
                }
                cout<<output<<endl;
                output.clear();
            }
            file.clear();
            file_end = file.tellg();
        }
        file.seekg( 0, ios::end );
        new_end = file.tellg();
        file.close();
    }else{
        cout << "Unable to open file";
    }
}
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