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Function that returns the max of a variable number of scalars

krad23 (13)
I need to create a function that takes as an input a variable number of scalars and returns the biggest one. Just like std::max() does for 2 elements, but I need it for an undefined number of elements, can be 2, or 5, or 10 etc.. Any suggestions on how to approach this?

What I need it for: I'm working with a bunch of vectors, maps, etc. and I need to find out which has the most elements. So I was thinking that I should end up with something like
int biggest = max(vector1.size(), vector2.size(), map1.size(), ...);
Last edited on
Peter87 (11175)
You can use std::max on multiple values.
 
 
std::max({2, 8, 5, 3}) // returns 8


If you want to find out the maximum number in a container you use std::max_element.
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std::vector v{2, 8, 5, 3};
std::max_element(v.begin(), v.end()) // returns 8


http://en.cppreference.com/w/cpp/algorithm/max
http://en.cppreference.com/w/cpp/algorithm/max_element
MiiNiPaa (8886)
std::max_element(v.begin(), v.end()) // returns 8
max_element returns iterator. You need to dereference result to get value.
krad23 (13)
None worked. I'm using VS2010

std::max({2, 8, 5, 3})
Error: no instance of overloaded function "std::max" matches the argument list

std::vector<int> v {2, 8, 5, 3};
Error: expected a ; (after v)

And more important, if I put this into a function, how do I have a variable number of inputs and how do I call them?
Last edited on
krad23 (13)
solved

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int maxof(int nargs, ...)
{
    va_list ap;
    va_start(ap, nargs);
    
    int max = va_arg(ap, int);
    
    for(int i = 2; i <= nargs ; i++) 
    {
        int a = va_arg(ap, int);
        if(a > max) max = a;
    }
    
    va_end(ap);
    
    return max;
}
MiiNiPaa (8886)
int maxof(int nargs, ...)
Do not use ellipsis. It is dangerous and useless in your case. How would you read n values from input (where n is not known beforehand) and then find maximum?
krad23 (13)
the n is known, i can find it. but it's variable
MiiNiPaa (8886)
but it's variable
And you cannot actually pass variable number of arguments to function. Number of arguments should be known ar compile time.

If you store elements in a vector you should use std::max_element:

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


int main()
{
	std::vector<int> v;
	//Solving lack of uniform initialization in VS2010
	v.push_back(4);
	v.push_back(2);
	v.push_back(12);
	v.push_back(6);
	// max_element returns iterator to found element
	//            ↓                so we need to dereference it
	int largest = * std::max_element(v.begin(), v.end());
	std::cout << largest;
}
 
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JLBorges (13770)
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#include <iostream>
#include <string>
#include <type_traits>

template < typename A, typename B >
typename std::common_type<A,B>::type maxv( A&& a, B&& b ) { return a<b ? b : a ; }

template < typename FIRST, typename... REST >
typename std::common_type<FIRST,REST...>::type maxv( FIRST&& first, REST&&... rest )
{ return maxv( first, maxv( std::forward<REST>(rest)... ) ) ; }

int main()
{
    const std::string str = "mnopqr" ;
    const char cstr[] = "uvwxyz" ;
    
    std::cout << maxv( 233, 23.8, 1200LL, 675243LL, 'A', 123456, short(32) ) << '\n'
              << maxv( str, cstr, "abcdef", std::string( 5, '!' ) ) << '\n' ;
              
    static_assert( std::is_same< std::string, decltype( maxv( str, cstr ) ) >::value , "unexpected" ) ;
}

http://coliru.stacked-crooked.com/a/0555fc26cf48cf33
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