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I need to sort a txt file by date, I need to work with the info stored in a vector, then sort it. I made a function that opens the file and stores all the lines in the vector "contents". I'm using visual studio code.

The code I got:

#include <iostream>
#include <fstream>
#include <string>
#include <stdio.h>
#include <vector>
using namespace std;


int readFile(){
    ifstream file;
    string filename = "searches.txt";
    string line;

    file.open(filename);

    vector<string> contents;

    while(!file.eof()){
        getline(file, line);
        contents.push_back(line);
    }

    for (auto file_line : contents)
        cout << file_line << endl;
 
    file.close();
    return 0;
}


int main(){
    readFile();
    
    return 0;
};

The actual output looks like this:

Oct 9 10:32:24 423.2.230.77:6166 Failed password for illegal user guest
Aug 28 23:07:49 897.53.984.6:6710 Failed password for root
Aug 4 03:18:56 960.96.3.29:5268 Failed password for admin
Jun 20 13:39:21 118.15.416.57:4486 Failed password for illegal user guest
Jun 2 18:37:41 108.57.27.85:5491 Failed password for illegal user guest
Oct 1 07:22:46 450.25.888.72:5978 Illegal user
Sep 14 10:01:55 694.78.591.36:5537 Failed password for illegal user guest
Jun 16 22:09:01 84.88.502.53:6452 Failed password for illegal user test
Sep 24 17:22:12 311.49.840.89:4145 Failed password for illegal user guest
Jul 12 20:17:38 390.18.339.91:6610 Failed password for root
Jul 16 03:38:22 990.87.715.21:6558 Failed password for admir/
Oct 26 00:53:10 505.13.173.18:4083 Failed password for illegal user guest

How can I sort the vector content by date ?

Andrej Podzimek
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Diego Michel
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    Side note: [Why is iostream::eof inside a loop condition (i.e. `while (!stream.eof())`) considered wrong?](https://stackoverflow.com/q/5605125/12149471) – Andreas Wenzel Jul 10 '23 at 01:09
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    Here's how to figure this out, this always works! Take out a blank sheet of paper. Write down a step-by-step process of doing this, as short, brief sentences in plain words. [Have your rubber duck review your plan](https://en.wikipedia.org/wiki/Rubber_duck_debugging). Generally, we don't write code for other people, on Stackoverflow. We always refer such questions to their rubber duck. After your rubber duck approves your proposed plan of action, simply take what you've written down and translate it directly into C++, and you're done! Have you discussed this with your rubber duck, yet? – Sam Varshavchik Jul 10 '23 at 01:22
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    You know how to read each line of the file and store it, now you just need to sort the lines. Use [`std::sort()`](https://en.cppreference.com/w/cpp/algorithm/sort) with a predicate that sorts based on criteria you specify. You can use [`std::istringstream`](https://en.cppreference.com/w/cpp/io/basic_istringstream) with [`std::get_time()`](https://en.cppreference.com/w/cpp/io/manip/get_time) to parse the leading date/time of each line. – Remy Lebeau Jul 10 '23 at 01:24
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    why on earth did you use such a terrible date format in a text log file? Prefix the line with the [ISO-8601 string](https://en.wikipedia.org/wiki/ISO_8601) would be much better, sorting can be done just by normal string sorting – phuclv Jul 10 '23 at 01:41
  • Why do you want to do this in C++ in the first place? This is a perfect fit for `sort`, provided that you make the date format reasonable first (i.e. replace the months by numbers) and then sort by the first 3 columns. – Andrej Podzimek Jul 10 '23 at 13:01
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    Side note: The line `file.close();` is redundant. When the `file` object gets destroyed, if it represents an open file, then the file will automatically be closed. – Andreas Wenzel Jul 10 '23 at 22:56

2 Answers2

1

You can use std::sort to sort all elements in your std::vector<std::string>.

However, by default, std::sort will call std::string::operator< to determine whether one object is smaller than another. This function will only perform a lexicographical comparison of both strings. This is not what you want. You want the strings to be sorted by the date they contain. In order to prevent std::sort from using std::string::operator<, you will have to write your own comparison function and tell std::sort to use that function instead.

Here is an example:

#include <iostream>
#include <fstream>
#include <vector>
#include <map>
#include <string>
#include <sstream>
#include <algorithm>

struct custom_time
{
    int day;
    int month;
    int hour;
    int minute;
    int second;
};

void extract_time_from_line( const std::string& line, custom_time& t )
{
    static const std::map<std::string,int> months =
    {
        {"Jan",1},
        {"Feb",2},
        {"Mar",3},
        {"Apr",4},
        {"May",5},
        {"Jun",6},
        {"Jul",7},
        {"Aug",8},
        {"Sep",9},
        {"Oct",10},
        {"Nov",11},
        {"Dec",12}
    };

    std::istringstream ss{line};
    std::string month;
    char delim1, delim2;

    //parse the line
    ss >> month >> t.day >> t.hour >> delim1 >> t.minute >> delim2 >> t.second;

    //verify that parsing was successful
    if ( !ss || delim1 != ':' || delim2 != ':' )
        throw std::runtime_error( "Error parsing line!" );

    //convert month to number
    auto it = months.find( month );
    if ( it == months.end() )
        return throw std::runtime_error( "Invalid month found!\n" );
    t.month = it->second;
}

bool compare( const std::string& a, const std::string& b )
{
    custom_time ta, tb;

    extract_time_from_line( a, ta );
    extract_time_from_line( b, tb );

    //first compare by month
    if ( ta.month < tb.month )
        return true;
    if ( ta.month > tb.month )
        return false;

    //then compare by day
    if ( ta.day < tb.day )
        return true;
    if ( ta.day > tb.day )
        return false;

    //then compare by hour
    if ( ta.hour < tb.hour )
        return true;
    if ( ta.hour > tb.hour )
        return false;

    //then compare by minute
    if ( ta.minute < tb.minute )
        return true;
    if ( ta.minute > tb.minute )
        return false;

    //then compare by second
    if ( ta.second < tb.second )
        return true;
    if ( ta.second > tb.second )
        return false;

    //if both times are identical, return true
    return true;
}

int main() try
{
    std::string line;

    //open the file
    std::ifstream file( "searches.txt" );
    if ( !file )
        throw std::runtime_error( "Error opening file!" );

    std::vector<std::string> contents;

    //read the entire file into the vector
    while ( std::getline( file, line ) )
    {
        contents.push_back( line );
    }

    //sort the vector
    std::sort( contents.begin(), contents.end(), compare );

    //print the sorted content of the vector
    for (auto file_line : contents)
        std::cout << file_line << '\n';
}
catch ( const std::runtime_error& e )
{
    std::cerr << "Exception encountered: " << e.what() << '\n';
}

For the input stated in the question, this program has the following output:

Jun 2 18:37:41 108.57.27.85:5491 Failed password for illegal user guest
Jun 16 22:09:01 84.88.502.53:6452 Failed password for illegal user test
Jun 20 13:39:21 118.15.416.57:4486 Failed password for illegal user guest
Jul 12 20:17:38 390.18.339.91:6610 Failed password for root
Jul 16 03:38:22 990.87.715.21:6558 Failed password for admir/
Aug 4 03:18:56 960.96.3.29:5268 Failed password for admin
Aug 28 23:07:49 897.53.984.6:6710 Failed password for root
Sep 14 10:01:55 694.78.591.36:5537 Failed password for illegal user guest
Sep 24 17:22:12 311.49.840.89:4145 Failed password for illegal user guest
Oct 1 07:22:46 450.25.888.72:5978 Illegal user
Oct 9 10:32:24 423.2.230.77:6166 Failed password for illegal user guest
Oct 26 00:53:10 505.13.173.18:4083 Failed password for illegal user guest

However, parsing both lines every time std::sort calls the compare function is not very efficient. Therefore, it would be more efficient to parse every line only once, and to cache the parsing results:

#include <iostream>
#include <fstream>
#include <vector>
#include <map>
#include <string>
#include <sstream>
#include <algorithm>

struct custom_time
{
    int day;
    int month;
    int hour;
    int minute;
    int second;
};

void extract_time_from_line( const std::string& line, custom_time& t )
{
    static const std::map<std::string,int> months =
    {
        {"Jan",1},
        {"Feb",2},
        {"Mar",3},
        {"Apr",4},
        {"May",5},
        {"Jun",6},
        {"Jul",7},
        {"Aug",8},
        {"Sep",9},
        {"Oct",10},
        {"Nov",11},
        {"Dec",12}
    };

    std::istringstream ss{line};
    std::string month;
    char delim1, delim2;

    //parse the line
    ss >> month >> t.day >> t.hour >> delim1 >> t.minute >> delim2 >> t.second;

    //verify that parsing was successful
    if ( !ss || delim1 != ':' || delim2 != ':' )
        throw std::runtime_error( "Error parsing line!" );

    //convert month to number
    auto it = months.find( month );
    if ( it == months.end() )
        return throw std::runtime_error( "Invalid month found!\n" );
    t.month = it->second;
}

bool compare( const custom_time& a, const custom_time& b )
{
    //first compare by month
    if ( a.month < b.month )
        return true;
    if ( a.month > b.month )
        return false;

    //then compare by day
    if ( a.day < b.day )
        return true;
    if ( a.day > b.day )
        return false;

    //then compare by hour
    if ( a.hour < b.hour )
        return true;
    if ( a.hour > b.hour )
        return false;

    //then compare by minute
    if ( a.minute < b.minute )
        return true;
    if ( a.minute > b.minute )
        return false;

    //then compare by second
    if ( a.second < b.second )
        return true;
    if ( a.second > b.second )
        return false;

    //if both times are identical, return true
    return true;
}

int main() try
{
    std::string line;

    //open the file
    std::ifstream file( "searches.txt" );
    if ( !file )
        throw std::runtime_error( "Error opening file!" );

    struct string_entry
    {
        custom_time time;
        std::string str;
    };

    std::vector<string_entry> contents;

    //read and parse the entire file into the vector
    while ( std::getline( file, line ) )
    {
        auto& new_elem = contents.emplace_back();
        extract_time_from_line( line, new_elem.time );
        new_elem.str = std::move( line );
    }

    //sort the vector
    std::sort(
        contents.begin(), contents.end(),
        [](const string_entry& a, const string_entry& b)
        {
            return compare( a.time, b.time );
        }
    );

    //print the sorted content of the vector
    for ( auto& elem : contents )
        std::cout << elem.str << '\n';
}
catch ( const std::runtime_error& e )
{
    std::cerr << "Exception encountered: " << e.what() << '\n';
}

This second program has the same output as the first program.

Andreas Wenzel
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0

It is rarely a good (or easy or fast) choice to implement plain text processing (which you need to make the text sortable) in C++. Bash is a much better fit for that purpose. You may still get a C++-like performance thanks to sort, not to mention the scalability of sort (and its capability to sort inputs larger than RAM).

  1. Make the date sortable.
  2. Sort the lines.
  3. Translate the date back to the original format.
#!/bin/bash
set -euo pipefail

declare -Ari months=([Jan]=1 [Feb]=2 [Mar]=3 [Apr]=4 [May]=5 [Jun]=6
                     [Jul]=7 [Aug]=8 [Sep]=9 [Oct]=10 [Nov]=11 [Dec]=12)
declare -a rmonths  # month numbers to month names
for month in "${!months[@]}"; do rmonths[months["$month"]]="$month"; done
declare -ar rmonths

# Make the date sortable.
while read -r month day rest; do
  printf '%02d %02d %s\n' "${months["$month"]}" "$day" "$rest"
done |

# Sort the lines.
sort |

# Translate the date back to the original format.
while read -r month day rest; do
  printf '%s %d %s\n' "${rmonths[$((10#"$month"))]}" "$((10#"$day"))" "$rest"
done
Andrej Podzimek
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