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std::qsort(3) C++ Standard Libary std::qsort(3) NAME std::qsort - std::qsort Synopsis Defined in header <cstdlib> void qsort( void *ptr, std::size_t count, std::size_t size, /* c-compare-pred */* comp ); (1) void qsort( void *ptr, std::size_t count, std::size_t size, /* compare-pred */* comp ); extern "C" using /* c-compare-pred */ = int(const void*, const void*); (2) (exposition only*) extern "C++" using /* compare-pred */ = int(const void*, const void*); Sorts the given array pointed to by ptr in ascending order. The ar- ray contains count elements of size bytes. Function pointed to by comp is used for ob- ject comparison. If comp indicates two elements as equivalent, their order is unspec- ified. If the type of the elements of the array is not a PODType (until C++11) TriviallyCopyable type (since C++11), the behavior is undefined. Parameters ptr - pointer to the array to sort count - number of elements in the array size - size of each element in the array in bytes comparison function which returns a negative integer value if the first argument is less than the second, a positive integer value if the first argument is greater than the second and zero if the argu- ments are equivalent. The signature of the comparison function should be equiva- lent to the following: comp - int cmp(const void *a, const void *b); The function must not modify the objects passed to it and must return consistent results when called for the same objects, regard- less of their positions in the array. Return value (none) Notes Despite the name, C++, C, and POSIX standards do not require this function to be implemented using Quicksort or make any complexity or stability guarantees. The two overloads provided by the C++ standard library are distinct because the types of the parameter comp are distinct (language linkage is part of its type). Example The following code sorts an array of integers using qsort(): // Run this code #include <array> #include <climits> #include <compare> #include <cstdlib> #include <iostream> int main() { std::array a{-2, 99, 0, -743, INT_MAX, 2, INT_MIN, 4}; std::qsort ( a.data(), a.size(), sizeof(decltype(a)::value_type), [](const void* x, const void* y) { const int arg1 = *static_cast<const int*>(x); const int arg2 = *static_cast<const int*>(y); const auto cmp = arg1 <=> arg2; if (cmp < 0) return -1; if (cmp > 0) return 1; return 0; } ); for (int ai : a) std::cout << ai << ' '; std::cout << '\n'; } Output: -2147483648 -743 -2 0 2 4 99 2147483647 Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 405 C++98 the elements of the array could have any type limited to PODType See also bsearch searches an array for an element of unspecified type (function) sort sorts a range into ascending order (function template) is_trivial checks if a type is trivial (C++11) (class template) C documentation for qsort http://cppreference.com 2024.06.10 std::qsort(3)
NAME | Synopsis | Parameters | Return value | Notes | Example | Output: | See also
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