C ++ std :: sort函数未完成？

Question

im currently setting up the highscore-part for a game and I have a very weird problem because of the weird behaviour of the std::sort function.

Im doing the whole thing in RAD Studio 10.2 (Embarcadero IDE) in C++.

So he is my code:

std::string Line;
int count = 0;
int i = 0;
ifstream File("Highscore.txt");
if(File.is_open())
{
    while(getline(File, Line))
    {
        count += 1;

    }

    File.close();

}

ifstream ReadFile("Highscore.txt");
if(ReadFile.is_open())
{
    string *scores = NULL;
    scores = new string[count];

    while(getline(ReadFile, Line))
    {
        scores[i] = Line;
        i += 1;
    }

    ReadFile.close();


    std::sort(scores, (scores+count));

    UnicodeString Uscores1 = scores[0].c_str();
    UnicodeString Uscores2 = scores[1].c_str();
    UnicodeString Uscores3 = scores[2].c_str();
    UnicodeString Uscores4 = scores[3].c_str();
    UnicodeString Uscores5 = scores[4].c_str();
    LScore1->Caption = Uscores1;
    LScore2->Caption = Uscores2;
    LScore3->Caption = Uscores3;
    LScore4->Caption = Uscores4;
    LScore5->Caption = Uscores5;

}

I get no errors from the compiler/linker and everything work should fine. The string array gets filled correctly and so on.

But its not sorting.

To show the problem to you I made a screenshot - on the left you can see the txtfile with the scores; on the right you can see the output after the sorting algorithm:

My question now is why this is happening?

Thanks for you help

Answer 1

Welcome to C++. Since you want to list numbers by rank, read them as int not string . Forget about operator new . You will not need it for years, if ever. Use standard containers like std::vector , which take care of the memory allocation and de-allocation transparently.

#include <iostream>
#include <vector>
#include <fstream>
#include <algorithm>
int main() {
    using namespace std;
    vector<int> scores;
    {
        ifstream inp("Highscore.txt");
        int next;
        while (inp >> next) {
            scores.push_back(next);
        }
    }
    sort(scores.begin(), scores.end());
    for (auto s : scores) {
        cout << s << '\n';
    }
    return 0;
}

Answer 2

How about something like:

int i = 0;
int * scoresInteger = NULL;
scoresInteger = new int[count];
for(i = 0; i < count; i++)
{
    scoresInteger[i] = std::stoi(scores[i]);
}
std::sort(scoresInteger, scoresInteger + count);

If you need to, you can convert the integers back into strings using targetStrings[i] = std::to_string(scoresInteger[i]) .

string * targetScores = NULL;
targetScores = new std::string[count];
for(i = 0; i < count; i++)
{
    targetScores[i] = std::to_string(scoresInteger[i]);
}
delete [] scoresInteger;
scoresInteger = NULL;

Don't forget to delete [] targetScores later.

Answer 3

My question now is why this is happening?

Because your scores are compared as string s and not as int s. Because of that "3" is greater that "25"

std::cout << std::boolalpha << (std::string("3") > std::string("25")) << std::endl; // true

Luckily you can pass a custom comparator (or lambda) to the std::sort to make it behave just as you want:

#include <iostream>
#include <string>
#include <algorithm>

int main()
{
    const int count = 5;
    std::string scores[count] = { "35","25","3","4","5" };

    // TWEAKED SORT
    std::sort(scores, scores + count, [](std::string const &s1, std::string const &s2)
    {
        return std::stoi(s2) < std::stoi(s1);
    });

    // TEST
    for (auto const &s : scores)
    {
        std::cout << s << std::endl;
    }
}

The compared string s in the above example are converted to int s and then compared, resulting in the desired sorting order .

35
25
5
4
3

Please note that I do not agree with the rest of your code and I think you should rethink the implementation, as it would be much easier, safer and more efficient to use std::vector<std::string> for your task.