passing a std::list to function

[jamesfarrow]

I am trying to learn abouts lists. Can any on help me with my functions. I would like to pass my list to a function that sorts it using std::sort then I can display the sorted list with another function.

Thanks in advance!

  
#include <iostream>
#include <list>
#include <cmath>
#include <algorithm>

//void sortList(std::list<int> &list);
//void editList(std::list<int> &list);
void showList(std::list<int> &list, std::list<int>::iterator, std::list<int>::iterator);


int main(int argc, const char * argv[]) {
    
    std::list<int> randomNumbers;
    srand(static_cast<unsigned int>(time(NULL)));
    
    
    //fill list with random integers and display
    for(int i = 0; i < 20; i++){
        randomNumbers.push_back(1 + rand() % 50);
    }
    std::list<int>::iterator itStart = randomNumbers.begin();
    std::list<int>::iterator itEnd = randomNumbers.end();
    
    //display unsorted list
    std::cout << "Unsorted list:" << std::endl;
    for(std::list<int>::iterator it = randomNumbers.begin(); it != randomNumbers.end(); it++){
        std::cout << *it << " ";
    }
    
    
    //sortList(randomNumbers);
    showList(randomNumbers, itStart, itEnd);
    
    
    return 0;
}

//
//void sortList(std::list<int> &list, std::list<int>::iterator start, std::list<int>::iterator end){
//    
//    std::sort(list.begin(), list.end());
//
//}

void showList(std::list<int> &list,std::list<int>::iterator start, std::list<int>::iterator end){
    
    std::cout << "\nThe list:" << std::endl;
    
    for(std::list<int>::iterator it = start; it != end; it++){
        std::cout << *it << " ";
    }
    std::cout << std::endl;
}

[48T7M4Gy]

#include <iostream>
#include <list>
#include <algorithm>

void sortList(std::list<int> &list);
void showList(const std::list<int> &);

int main(int argc, const char * argv[]) {
    
    std::list<int> randomNumbers;
    
    
    //fill list with random integers and display
    srand(static_cast<unsigned int>(time(NULL)));
    for(int i = 0; i < 20; i++){
        randomNumbers.push_back(1 + rand() % 50);
    }
    
    //display unsorted list
    std::cout << "Unsorted list:" << std::endl;
    showList(randomNumbers);
    
    // SORT LIST
    sortList(randomNumbers);
    
    // DISPLAY SORTED LIST
    std::cout << "Sorted list:" << std::endl;
    showList(randomNumbers);
    
    return 0;
}

void showList(const std::list<int> &aList){
    for(auto it: aList){
        std::cout << it << ' ';
    }
    std::cout << '\n';
}


void sortList(std::list<int> &aList){
    aList.sort();
}

Unsorted list:
20 16 42 40 41 38 26 40 27 12 36 15 44 42 28 13 32 16 49 15 
Sorted list:
12 13 15 15 16 16 20 26 27 28 32 36 38 40 40 41 42 42 44 49 
Program ended with exit code: 0

http://en.cppreference.com/w/cpp/container/list/sort

[gunnerfunner]

and to add to kemort's, as ever, excellent reply OP you can't do this:

 std::sort(list.begin(), list.end());

because std::sort requires random-access iterators whereas the list.begin(), list.end() iterators are bi-directional types - all random access iterators are also bidirectional but the reverse is not true
std::sort(): http://en.cppreference.com/w/cpp/algorithm/sort
list.begin(): http://www.cplusplus.com/reference/list/list/begin/
bi-directional iterator: http://www.cplusplus.com/reference/iterator/BidirectionalIterator/

[JLBorges]

To sort a std::list using std::sort, we would have to resort to an indirect sort.

const std::list<int> seq { 5, 9, 3, 2, 7, 1, 4, 8, 0, 6 } ;

// indirect sort with std::sort
// http://en.cppreference.com/w/cpp/utility/functional/reference_wrapper
std::vector< std::reference_wrapper<const int> > refs( std::begin(seq), std::end(seq) ) ;
std::sort( std::begin(refs), std::end(refs) ) ;

for( int v : refs ) std::cout << v << ' ' ;
std::cout << '\n' ;

http://coliru.stacked-crooked.com/a/1a8103553cb44c62

The recommended way to sort std::list (direct sort) is to use the member function sort()
http://en.cppreference.com/w/cpp/container/list/sort
Though the cppreference page doesn't mention it, the complexity is:
"Approximately N log(N) comparisons, where N == size()"

std::list<int> seq { 5, 9, 3, 2, 7, 1, 4, 8, 0, 6 } ;

// (direct) stable sort with list::sort
seq.sort() ; // http://en.cppreference.com/w/cpp/container/list/sort

for( int v : seq ) std::cout << v << ' ' ;
std::cout << '\n' ;

http://coliru.stacked-crooked.com/a/1a8103553cb44c62

[jamesfarrow]

Excellent! Thanks very much everyone for your help, not sure why I couldn't get i to work but it does now - thanks again!

[Cubbi]

Though the cppreference page doesn't mention it,

does now

[jamesfarrow]

just a few more things please - I'm trying to pehaps be a bit ambitious and over reach... Ive added some insert and erase functions, but they don't seem to have the desired effect!! It sjust something I want to try and get working

Thanks in advance

#include <iostream>
#include <list>
#include <cmath>
#include <algorithm>

void sortList(std::list<int> &list);
void editList(std::list<int> &list);
void showList(std::list<int> &alist);


int main(int argc, const char * argv[]) {
    
    std::list<int> randomNumbers;
    srand(static_cast<unsigned int>(time(NULL)));
    int sentinel = 0;
    
    
    //fill list with random integers and display
    for(int i = 0; i < 5; i++){
        randomNumbers.push_back(1 + rand() % 50);
    }
    
    //display unsorted list
    std::cout << "Unsorted list:" << std::endl;
    for(std::list<int>::iterator it = randomNumbers.begin(); it != randomNumbers.end(); it++){
        std::cout << *it << " ";
    }
    
    do{
        
        std::cout << "\n1 to sort list" << std::endl;
        std::cout << "2 to display list" << std::endl;
        std::cout << "3 to edit list" << std::endl;
        std::cout << "-1 to end. Selection: ";
        std::cin >> sentinel;
        while( (!std::cin) || (sentinel < -1 || sentinel > 3 )){
            std::cin.clear();
            std::cin.ignore();
            std::cout << "-1 to end. Please select: ";
            std::cin >> sentinel;
        }
        
        switch (sentinel) {
            case 1:
                std::cout << "case 1" << std::endl;
                sortList(randomNumbers);
                break;
            case 2:
                std::cout << "case 2" << std::endl;
                showList(randomNumbers);
                break;
            case 3:
                std::cout << "case 3" << std::endl;
                editList(randomNumbers);
                break;
            default:
                std::cout << "Not a choice!" << std::endl;
                break;
        }
    }while(sentinel != -1);
    
    
    return 0;
}


void sortList(std::list<int> &alist){
    
    alist.sort();

}

void showList(std::list<int> &list){
    
    std::cout << "\nThe list:" << std::endl;
    
    for( auto it : list){
        std::cout << it << " ";
    }
    std::cout << std::endl;
}

void editList(std::list<int> &aList){
    
    int sentinel = 0;
        
        std::cout << "\n1 to push_front" << std::endl;
        std::cout << "2 to push_back" << std::endl;
        std::cout << "3 to insert" << std::endl;
        std::cout << "4 to erase" << std::endl;
        std::cout << "-1 to end. Selection: ";
        std::cin >> sentinel;
        while( (!std::cin) || (sentinel < -1 || sentinel > 4 )){
            std::cin.clear();
            std::cin.ignore();
            std::cout << "-1 to end. Please select: ";
            std::cin >> sentinel;
        }
        
        switch (sentinel) {
            case 1:
                std::cout << "Input number to push_front: " << std::endl;
                int number;
                std::cin >> number;
                aList.push_front(number);
                break;
            case 2:
                std::cout << "Input number to push_back: " << std::endl;
                std::cin >> number;
                aList.push_back(number);
                break;
            case 3:
                std::cout << "Input position and number to insert: " << std::endl;
                std::cout << "Postion: ";
                int position;
                std::cin >> position;
                std::cout << "Number: ";
                std::cin >> number;
                for( std::list<int>::iterator it = aList.begin(); it != aList.end(); it++){
                    if(*it == position){
                        aList.insert(it, number);
                    }
                }
                break;
            case 4:
                std::cout << "Input position to erase: " << std::endl;
                std::cout << "Postion: ";
                std::cin >> position;
                for( std::list<int>::iterator it = aList.begin(); it != aList.end();){
                    if(*it == position){
                        it = aList.erase(it);
                    }
                    else{
                        it++;
                    }
                }
                break;
            default:
                std::cout << "Not a choice!" << std::endl;
                break;
        }
    
    
    
}

[jamesfarrow]

Sorry - I've been having a bad day. After a long hard look at what I was doing I have realised that my code is ok - just me that is wrong.

As a rule of thumb - I'm not usually that stupid 😂


Thanks again for all of your help.