Standard C library provides qsort function that can be used for sorting an array. Following is the prototype of qsort() function. // Sort an array of any type. The parameters are base // address of array size of array and pointer to // comparator function void qsort (void* base size_t num size_t size int (*comparator)(const void* const void*));
It requires a pointer to the array the number of elements in the array the size of each element and a comparator function. We have discussed qsort comparator in detail her . C ++ standardbibliotek giver en lignende funktionssortering (), der stammer fra STL. Vi har diskuteret C ++ slags her . Following are prototypes of C++ sort() function. // To sort in default or ascending order. template void sort(T first T last); // To sort according to the order specified // by comp. template void sort(T first T last Compare comp);
The order of equal elements is not guaranteed to be preserved. C++ provides std::stable_sort that can be used to preserve order. Sammenligning med qsort og sortering () 1. Implementeringsdetaljer: Som navnet antyder, bruger QSORT -funktion QuickSort -algoritme til at sortere det givne array, selvom C -standarden ikke kræver, at den implementerer QuickSort. C ++ sorteringsfunktion bruger introsort, som er en hybridalgoritme. Forskellige implementeringer bruger forskellige algoritmer. GNU-standard C ++ -biblioteket bruger for eksempel en 3-delt hybrid-sorteringsalgoritme: Introsort udføres først (Introsort i sig selv som en hybrid af Quicksort og Heap Sort) efterfulgt af en indsættelsessortering på resultatet. 2. Kompleksitet: C -standarden taler ikke om dens kompleksitet af QSort. Den nye C ++ 11 -standard kræver, at kompleksiteten af sortering er O (nlog (n)) i værste tilfælde. Tidligere versioner af C ++ såsom C ++ 03 muliggør mulige værste tilfælde af O (N^2). Kun gennemsnitlig kompleksitet var påkrævet for at være O (n log n). 3. kørselstid: STL’s sort ran faster than C’s qsort because C++’s templates generate optimized code for a particular data type and a particular comparison function. STL’s sort runs 20% to 50% faster than the hand-coded quicksort and 250% to 1000% faster than the C qsort library function. C might be the fastest language but qsort is very slow. When we tried to sort one million integers on C++14 Time taken by C qsort() was 0.247883 sec and time taken by C++ sort() was only 0.086125 sec CPP // C++ program to demonstrate performance of // C qsort and C++ sort() algorithm #include using namespace std; // Number of elements to be sorted #define N 1000000 // A comparator function used by qsort int compare(const void * a const void * b) { return ( *(int*)a - *(int*)b ); } // Driver program to test above functions int main() { int arr[N] dupArr[N]; // seed for random input srand(time(NULL)); // to measure time taken by qsort and sort clock_t begin end; double time_spent; // generate random input for (int i = 0; i < N; i++) dupArr[i] = arr[i] = rand()%100000; begin = clock(); qsort(arr N sizeof(int) compare); end = clock(); // calculate time taken by C qsort function time_spent = (double)(end - begin) / CLOCKS_PER_SEC; cout << 'Time taken by C qsort() - ' << time_spent << endl; time_spent = 0.0; begin = clock(); sort(dupArr dupArr + N); end = clock(); // calculate time taken by C++ sort time_spent = (double)(end - begin) / CLOCKS_PER_SEC; cout << 'Time taken by C++ sort() - ' << time_spent << endl; return 0; }
Time taken by C qsort() - 0.247883 Time taken by C++ sort() - 0.086125
C++ sort() is blazingly faster than qsort() on equivalent data due to inlining. sort() on a container of integers will be compiled to use std::less::operator() by default which will be inlined and sort() will be comparing the integers directly. On the other hand qsort() will be making an indirect call through a function pointer for every comparison which compilers fails to optimize. 4. fleksibilitet: STLs sortering fungerer for alle datatyper og for forskellige databeholdere som C Arrays C ++ Vectors C ++ deques osv. Og andre containere, der kan skrives af brugeren. Denne form for fleksibilitet er ret vanskelig at opnå i C. 5. Sikkerhed: Sammenlignet med QSORT er den templerede slags mere typesikker, da den ikke kræver adgang til dataelementer gennem usikre ugyldige pointer, som QSORT gør. Referencer: http://theory.stanford.edu/~amitp/rants/c++-vs-c/ https://en.wikipedia.org/wiki/sort_(c%2B%2B)
