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 šeit Apvidū C ++ standarta bibliotēka nodrošina līdzīgu funkciju veidu (), kas radusies STL. Mēs esam apsprieduši c ++ šķirošanu šeit . 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. Salīdzinājums ar QSort un Kort () 1. Ievietošanas informācija: Tā kā nosaukums norāda, ka QSORT funkcija izmanto QuickSort algoritmu, lai sakārtotu doto masīvu, lai gan C standartam nav nepieciešams, lai tas ieviestu QuickSort. C ++ kārtošanas funkcija izmanto introsort, kas ir hibrīda algoritms. Dažādās ieviešanā tiek izmantoti dažādi algoritmi. Piemēram, GNU standarta C ++ bibliotēkā tiek izmantots trīsdaļīgs hibrīda šķirošanas algoritms: introsort tiek veikts vispirms (introsort pats ir QuickSort un Heap Sort hibrīds), kam seko rezultāta ievietošana. 2. sarežģītība: C standarts nerunā par QSORT sarežģītību. Jaunais C ++ 11 standarts prasa, lai vissliktākajā gadījumā būtu O (Nlog (n)) sarežģītība. Iepriekšējās C ++ versijas, piemēram, C ++ 03, ļauj iespējamo sliktākā O (n^2) scenāriju. Bija nepieciešama tikai vidējā sarežģītība O (n log n). 3. skriešanas laiks: 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. Elastība: STL STL darbojas visiem datu tipiem un dažādiem datu konteineriem, piemēram, C blokiem C ++ vektoriem C ++ Deques utt. Un citus konteinerus, kurus var rakstīt lietotājs. Šāda veida elastību ir diezgan grūti sasniegt C. 5. Drošība: Salīdzinot ar QSORT, veidotais veids ir drošāks, jo tas neprasa piekļuvi datu vienumiem, izmantojot nedrošus tukšos rādītājus, kā to dara QSORT. Atsauces: http://theory.stanford.edu/~amitp/rants/c++-vs-c/ https://en.wikipedia.org/wiki/sort_(c%2B%2B)
