c++ std::sort uses custom comparison function sorting method

Use sort to sort elements in container

The std::sort() function is specifically used to sort elements within a specified range in a container or ordinary array. The sorting rules are sorted in ascending order by default by the size of the element value.
sort() only provides support for array, vector, and deque containers
You can customize the sorting function

#include <iostream>
#include <vector>
#include <algorithm>

// Define the pair type
typedef std::pair<uint32_t, uint64_t> PairType;

// Comparator function to compare pairs based on the second element (value)
bool comparePairs(const PairType& p1, const PairType& p2) {
    return  > ;
}

int main() {
    // Create the vector of pairs
    std::vector<PairType> vec = {
        {1, 100},   // idx=1, value=100
        {2, 50},    // idx=2, value=50
        {3, 200},   // idx=3, value=200
        // Add more pairs here if needed
    };

    // Sort the vector using the comparator function
    std::sort((), (), comparePairs);

    // Output the sorted vector
    for (const auto& pair : vec) {
        std::cout << "idx: " <<  << ", value: " <<  << std::endl;
    }

    return 0;
}

comparePairs is our custom function, sort the third place

 std::sort((), (), comparePairs);

How to call custom member functions in class to sort

typedef std::pair&lt;uint32_t, uint64_t&gt; PairType;

bool MySort::comparePairs(const PairType&amp; p1, const PairType&amp; p2) {
    return  &gt; ;
}

bool MySort::sort_fun(vector&lt;PairType&gt; vec)
{
    std::sort((), (), comparePairs); //Report an error}

Visual Studio error:

C3867   “MySort::compareParis”: non-standard syntax; please use "&" to create a pointer to a member
C2672   “std::sort”: No matching overloaded function was found
C2780   “void std::sort(const _RanIt,const _RanIt)”: 2 parameters should be entered, but 3 parameters should be provided

Cause of error

This error is because when using std::sort(), a member function pointer is passed, not a normal function pointer

Solution

Using Lambda expressions:

Modified code:

typedef std::pair&lt;uint32_t, uint64_t&gt; PairType;

bool MySort::comparePairs(const PairType&amp; p1, const PairType&amp; p2) {
    return  &gt; ;
}

bool MySort::sort_fun(vector&lt;PairType&gt; vec)
{
	// Define Lambda expressions	auto sortLambda = [this](const PairType&amp; p1, const PairType&amp; p2) {
        return this-&gt;comparePairs(a, b);
    };
    
	std::sort((), (), sortLambda); 
}

Summarize

The above is personal experience. I hope you can give you a reference and I hope you can support me more.