Thread: Issue with function pointer and template

The template at the top is giving me an error when I go to compile using the sort function. My guess is the compiler needs to know what data types are going to be used at compile time.

Is there a workaround?

Code:

// VectorApp1.cpp : Defines the entry point for the console application.       //


#include "stdafx.h"
#include <iostream>
#include <vector>
#include <cstdlib>
#include <ctime>
#include <algorithm>


//template <typename lhs, typename rhs>
//bool isLhsLessRhsFunc(lhs, rhs) { return (lhs<rhs); }


bool isLhsLessRhsFunc(int lhs, int rhs) { return (lhs<rhs); }


int main()
{
	std::vector<int> testVec;
	
	std::cout << "Size of vec: " << testVec.size() << std::endl;


	std::srand(std::time(0)); // use current time as seed for random generator


	for (int i = 0; i < 10000; i++)
	{
		testVec.push_back(std::rand());
	}


	for (auto it = testVec.begin(); it != testVec.end(); ++it)
	{
		std::cout << *it << '\n';
	}


	std::cout << "Size of vec: " << testVec.size() << std::endl;


	std::sort(testVec.begin(), testVec.end(), isLhsLessRhsFunc);


	for (auto it = testVec.begin(); it != testVec.end(); ++it)
	{
		std::cout << *it << '\n';
	}


    return 0;
}

Thanks for the help, and I can get it to work like that, but I'm trying to get it to work more abstractly, if that is a word.

templates - C++ Get Vector type - Stack Overflow

They are using a template of a template and that would be pretty slick at least in my eyes, but I haven't been able to get it compile for me.

Trying to be too clever has been the downfall of many great programmers.... I'm assuming.

Ok, I used some of functions in the vector container library, a lambda function and the std::less function. The replies have been helpful.

There is a lot of syntax to learn in C++, that's for sure.

Code:

#include <vector>#include <cstdlib>
#include <ctime>
#include <algorithm>


auto isLhsLessRhsFunc = [](auto a, auto b) { return a < b; };


template <typename T>
void printContainer(T a) 
{ 
	for(auto it = a.begin(); it != a.end(); ++it)
	{
		std::cout << *it << '\n';
	}
}


int main()
{
	std::vector<int> testVec(10);
	std::vector<int> testVecToSwap{5};
		
	std::cout << "Size of vec: " << testVec.size() << std::endl;


	std::srand(std::time(0)); // use current time as seed for random generator
	
	for (auto it = testVec.begin(); it != testVec.end(); ++it)
	{
		*it = std::rand();
	}


	std::cout << "Vec Original content" << std::endl;
	printContainer(testVec);


	std::cout << "Size of vec: " << testVec.size() << std::endl;
	std::cout << "Max Size of vec: " << testVec.max_size() << std::endl;
	std::cout << "Capacity of vec: " << testVec.capacity() << std::endl;


	std::sort(testVec.begin(), testVec.end(), isLhsLessRhsFunc);


	std::cout << "Vec Sorted content" << std::endl;
	printContainer(testVec);


	std::random_shuffle(testVec.begin(), testVec.end());


	std::cout << "Vec Random content" << std::endl;
	printContainer(testVec);


	std::sort(testVec.begin(), testVec.end(), std::less<>());
	std::cout << "Vec Sorted content" << std::endl;
	printContainer(testVec);


	testVec.insert(testVec.begin(), 1);


	std::cout << "Vec Inserted content" << std::endl;
	printContainer(testVec);


	testVec.erase(testVec.begin());


	std::cout << "Vec Erased content" << std::endl;
	printContainer(testVec);


	testVec.pop_back();
	std::cout << "Vec popback" << std::endl;
	printContainer(testVec);


	testVec.swap(testVecToSwap);
	std::cout << "Vec swap: testVec" << std::endl;
	printContainer(testVec);


	std::cout << "Vec swap: testVecToSwap" << std::endl;
	printContainer(testVecToSwap);


	testVec.erase(testVec.begin(), testVec.end());
	std::cout << "Vec All Erased content" << std::endl;
	printContainer(testVec);
	
    return 0;
}