如何在 C++ 中比较多个 .txt 文件？

Question

I´ve made a program in which people create an auction which is then saved as a .txt file that looks like this:

Auction name: Books
Item to sell: Lord of the rings
Description: words........
Reserve price: 12

Then, on a separate project, I made a similar thing but with Bids which are also saved on a .txt file with the structure:

// "personName.txt"
24 ( <-- Example number of the person's bid)

The problem is that now I have to make multiple "bid" files and compare them with each other and the auction file to determine who won the auction.

How can this be accomplished?

Answer 1

I'm not sure why you'd do this task with files, as it is very expensive to load files into the program. However, your task can be accomplished (that is if I accurately understand what you're asking; your question was not written very clearly).

First, make sure to include your proper headers from the STL

#include <iostream>    // Assuming you have console IO functionality
#include <filesystem>  // Accessing all files in a directory for searching
#include <fstream>     // Loading files into the program
#include <string>      // Assuming you have names for bidders
#include <vector>      // Load the files' contents into a vector

As you may be able to somewhat tell from the includes and their explanations, here's my plan for the program:

1. Store all auction files in a directory that ONLY has auction files. This will save time because the program won't have to check a bunch of files that we aren't interested in.
2. Using std::filesystem::directory_iterator , search through all the files in the directory from above and save their contents to an std::vector
3. Use a max function to determine the largest bid and output their name

In practice, that means we may want a vector of structs that have (1) the name of the bidder and (2) their bid. Then we compare all their bids using a max function (like stated above). When we find the max, we will be able to very easily find the name bidder that goes with that bid and output to the screen.

The .txt files (for my solution) have strictly two lines per file. The first line is the bidder's name, and the second line is the bidder's bid. This will line up exactly with the struct we'll use for loading these files into the program.

So, here's the program (make sure you're using C++17 ):

#include <filesystem> // std::filesystem : path, directory_iterator, current_path, parent_path
#include <fstream>    // std::ifstream
#include <iomanip>    // std::setpercision
#include <iostream>   // std::cout, std::cerr, std::endl
#include <limits>     // std::numeric_limits
#include <string>     // std::string
#include <vector>     // std::vector

namespace fs = std::filesystem;

// The max size of a file stream saved into this variables
constexpr auto STREAM_MAX = std::numeric_limits<std::streamsize>::max();

// The directory to the folder with all the bidders in it
//   What I've done here is used the a folder in the same parent
//   directory as this file. So we go one step out of the 
//   current path, then go into the "bids" folder. However,
//   I compiled this in a different directory hierarchy, so I
//   commented the '.parent_path()' part out.
const auto BIDDING_PATH = 
    fs::path(fs::current_path()/*.parent_path()*/ / "bids");

/**
 This will be the struct we use in the vector

 @param name The name of the bidder
 @param bid  The price of the bidder's bid
*/
struct Bidder
{
    std::string name;
    double bid;

    // Define a constructor for std::vector::emplace_back
    Bidder(std::string name, double bid) :
        name(std::move(name)), bid(bid)
    {}
};

std::vector<Bidder> load_bids()
{
    std::vector<Bidder> all_bidders;

    // Loop through every file in the 'BIDDING_PATH' directory 
    // (not recursively)
    for (auto file : fs::directory_iterator(BIDDING_PATH))
    {
        std::ifstream cur_file(file.path().c_str());
        if (cur_file.is_open())
        { // Load file into a struct and add it to `all_bidders`
            std::string cur_name;
            double cur_bid;

            // Read the contents of the file into the above variables
            std::getline(cur_file, cur_name);
            cur_file >> cur_bid;

            // Now get rid of the newline character left behind by the '>>'
            // operator from 'cur_file >> cur_bid'
            cur_file.ignore(STREAM_MAX, '\n');

            // Add the bidder to the `all_bidders` vector
            all_bidders.emplace_back(cur_name, cur_bid);

            // Some debugging feedback
            std::cout 
                << "File loaded:   " << file.path().string()    << '\n'
                << "Bidder's name: " << all_bidders.back().name << '\n'
                << "Bidder's bid:  " << all_bidders.back().bid  << '\n'
                << std::endl;
        }
        else
        {
            std::cerr 
                << "Error opening file: " << file.path().string() 
                << std::endl;
        }
    }

    return all_bidders;
}

Bidder find_max_bidder(const std::vector<Bidder>& bidders)
{
    // Keeps track of the winning bidder
    // Intially set to a null value
    Bidder max_bidder("", -1.0);

    for (const auto& cur_bidder : bidders)
    {
        if (cur_bidder.bid > max_bidder.bid)
        {
            max_bidder.name = cur_bidder.name;
            max_bidder.bid  = cur_bidder.bid;
        }
    }

    // Check if no max was found
    if (max_bidder.bid == -1.0)
    {
        std::cerr
            << "Error: No max bidder was found\n"
            << "Are there any bidding files in the given directory?\n"
            << std::endl;
    }

    return max_bidder;
}

int main()
{
    // Load all bidders into the `all_bidders` vector, then
    // calculate the max bid
    std::vector<Bidder> all_bidders = load_bids();
    Bidder winning_bidder = find_max_bidder(all_bidders);

    // Print out the max bid
    std::cout
        << "The winner of this auction is " << winning_bidder.name << "!\n"
        << "They bid $" << winning_bidder.bid << std::setprecision(2) << "!\n"
        << std::endl;

    // Keep the console from closing
    std::cin.get();
    return 0;
}

Please note a few things:

• You need to compile this in C++17 ; I used MSVC with Visual Studio 2019
• There are additional #include s that weren't needed to explain our gameplan, but I added for formatting or making my life easier or something
• You can delete the portion under " // Some debugging feedback if you want
• I did not cover the first part of your question because it (1) didn't really seem like a question and (2) you didn't seem to be having any concerns with that part

Additionally, I generated a random set of data with this Batch file:

@echo off
setlocal EnableDelayedExpansion
set wkdir=!cd!
goto :begin

:begin
cd "..\bids"
set rand_bid=
for /l %%a in (1,1,100) do (
    echo Bidder%%a > bidder%%a.txt
    set /a rand_bid=!random! %% 1000
    echo !rand_bid!.00 >> bidder%%a.txt
)
cd !wkdir!
goto :end

:end
exit

After running that Batch file and then running my program, here was my output:

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder1.txt
Bidder's name: Bidder1
Bidder's bid:  219

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder10.txt
Bidder's name: Bidder10
Bidder's bid:  693

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder100.txt
Bidder's name: Bidder100
Bidder's bid:  275

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder11.txt
Bidder's name: Bidder11
Bidder's bid:  669

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder12.txt
Bidder's name: Bidder12
Bidder's bid:  720

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder13.txt
Bidder's name: Bidder13
Bidder's bid:  741

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder14.txt
Bidder's name: Bidder14
Bidder's bid:  342

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder15.txt
Bidder's name: Bidder15
Bidder's bid:  124

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder16.txt
Bidder's name: Bidder16
Bidder's bid:  627

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder17.txt
Bidder's name: Bidder17
Bidder's bid:  244

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder18.txt
Bidder's name: Bidder18
Bidder's bid:  61

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder19.txt
Bidder's name: Bidder19
Bidder's bid:  79

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder2.txt
Bidder's name: Bidder2
Bidder's bid:  979

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder20.txt
Bidder's name: Bidder20
Bidder's bid:  211

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder21.txt
Bidder's name: Bidder21
Bidder's bid:  168

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder22.txt
Bidder's name: Bidder22
Bidder's bid:  44

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder23.txt
Bidder's name: Bidder23
Bidder's bid:  902

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder24.txt
Bidder's name: Bidder24
Bidder's bid:  753

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder25.txt
Bidder's name: Bidder25
Bidder's bid:  975

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder26.txt
Bidder's name: Bidder26
Bidder's bid:  220

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder27.txt
Bidder's name: Bidder27
Bidder's bid:  576

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder28.txt
Bidder's name: Bidder28
Bidder's bid:  541

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder29.txt
Bidder's name: Bidder29
Bidder's bid:  249

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder3.txt
Bidder's name: Bidder3
Bidder's bid:  788

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder30.txt
Bidder's name: Bidder30
Bidder's bid:  661

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder31.txt
Bidder's name: Bidder31
Bidder's bid:  98

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder32.txt
Bidder's name: Bidder32
Bidder's bid:  307

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder33.txt
Bidder's name: Bidder33
Bidder's bid:  698

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder34.txt
Bidder's name: Bidder34
Bidder's bid:  287

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder35.txt
Bidder's name: Bidder35
Bidder's bid:  489

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder36.txt
Bidder's name: Bidder36
Bidder's bid:  685

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder37.txt
Bidder's name: Bidder37
Bidder's bid:  196

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder38.txt
Bidder's name: Bidder38
Bidder's bid:  321

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder39.txt
Bidder's name: Bidder39
Bidder's bid:  332

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder4.txt
Bidder's name: Bidder4
Bidder's bid:  267

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder40.txt
Bidder's name: Bidder40
Bidder's bid:  593

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder41.txt
Bidder's name: Bidder41
Bidder's bid:  485

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder42.txt
Bidder's name: Bidder42
Bidder's bid:  863

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder43.txt
Bidder's name: Bidder43
Bidder's bid:  869

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder44.txt
Bidder's name: Bidder44
Bidder's bid:  612

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder45.txt
Bidder's name: Bidder45
Bidder's bid:  165

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder46.txt
Bidder's name: Bidder46
Bidder's bid:  889

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder47.txt
Bidder's name: Bidder47
Bidder's bid:  554

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder48.txt
Bidder's name: Bidder48
Bidder's bid:  783

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder49.txt
Bidder's name: Bidder49
Bidder's bid:  747

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder5.txt
Bidder's name: Bidder5
Bidder's bid:  966

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder50.txt
Bidder's name: Bidder50
Bidder's bid:  322

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder51.txt
Bidder's name: Bidder51
Bidder's bid:  775

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder52.txt
Bidder's name: Bidder52
Bidder's bid:  306

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder53.txt
Bidder's name: Bidder53
Bidder's bid:  376

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder54.txt
Bidder's name: Bidder54
Bidder's bid:  895

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder55.txt
Bidder's name: Bidder55
Bidder's bid:  374

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder56.txt
Bidder's name: Bidder56
Bidder's bid:  166

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder57.txt
Bidder's name: Bidder57
Bidder's bid:  332

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder58.txt
Bidder's name: Bidder58
Bidder's bid:  665

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder59.txt
Bidder's name: Bidder59
Bidder's bid:  177

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder6.txt
Bidder's name: Bidder6
Bidder's bid:  888

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder60.txt
Bidder's name: Bidder60
Bidder's bid:  399

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder61.txt
Bidder's name: Bidder61
Bidder's bid:  271

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder62.txt
Bidder's name: Bidder62
Bidder's bid:  996

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder63.txt
Bidder's name: Bidder63
Bidder's bid:  487

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder64.txt
Bidder's name: Bidder64
Bidder's bid:  874

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder65.txt
Bidder's name: Bidder65
Bidder's bid:  499

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder66.txt
Bidder's name: Bidder66
Bidder's bid:  72

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder67.txt
Bidder's name: Bidder67
Bidder's bid:  902

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder68.txt
Bidder's name: Bidder68
Bidder's bid:  66

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder69.txt
Bidder's name: Bidder69
Bidder's bid:  64

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder7.txt
Bidder's name: Bidder7
Bidder's bid:  246

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder70.txt
Bidder's name: Bidder70
Bidder's bid:  167

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder71.txt
Bidder's name: Bidder71
Bidder's bid:  961

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder72.txt
Bidder's name: Bidder72
Bidder's bid:  250

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder73.txt
Bidder's name: Bidder73
Bidder's bid:  280

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder74.txt
Bidder's name: Bidder74
Bidder's bid:  185

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder75.txt
Bidder's name: Bidder75
Bidder's bid:  962

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder76.txt
Bidder's name: Bidder76
Bidder's bid:  174

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder77.txt
Bidder's name: Bidder77
Bidder's bid:  157

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder78.txt
Bidder's name: Bidder78
Bidder's bid:  221

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder79.txt
Bidder's name: Bidder79
Bidder's bid:  312

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder8.txt
Bidder's name: Bidder8
Bidder's bid:  189

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder80.txt
Bidder's name: Bidder80
Bidder's bid:  842

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder81.txt
Bidder's name: Bidder81
Bidder's bid:  415

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder82.txt
Bidder's name: Bidder82
Bidder's bid:  313

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder83.txt
Bidder's name: Bidder83
Bidder's bid:  220

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder84.txt
Bidder's name: Bidder84
Bidder's bid:  200

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder85.txt
Bidder's name: Bidder85
Bidder's bid:  738

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder86.txt
Bidder's name: Bidder86
Bidder's bid:  323

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder87.txt
Bidder's name: Bidder87
Bidder's bid:  529

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder88.txt
Bidder's name: Bidder88
Bidder's bid:  196

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder89.txt
Bidder's name: Bidder89
Bidder's bid:  991

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder9.txt
Bidder's name: Bidder9
Bidder's bid:  917

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder90.txt
Bidder's name: Bidder90
Bidder's bid:  441

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder91.txt
Bidder's name: Bidder91
Bidder's bid:  691

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder92.txt
Bidder's name: Bidder92
Bidder's bid:  578

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder93.txt
Bidder's name: Bidder93
Bidder's bid:  234

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder94.txt
Bidder's name: Bidder94
Bidder's bid:  638

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder95.txt
Bidder's name: Bidder95
Bidder's bid:  569

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder96.txt
Bidder's name: Bidder96
Bidder's bid:  267

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder97.txt
Bidder's name: Bidder97
Bidder's bid:  788

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder98.txt
Bidder's name: Bidder98
Bidder's bid:  790

File loaded:   C:\Dev\C++\Others\DevBox\Testing\bids\bidder99.txt
Bidder's name: Bidder99
Bidder's bid:  781

The winner of this auction is Bidder62 !
They bid $996!

I hope that helps! If you have any questions, feel free to ask!