Sort or Mergesort based on user input - c++

Question

I am trying to call a function based on user input. I cannt figure out what I am doing wrong. I keep getting this error
error: no matching function for call to 'sort(std::vector<int, std::allocator<int> >&)'
Can someone tell me what I am doing wrong. Please explain any suggestions thoroughly as I am brand new to C++. Here is my code:
#include <iterator>
#include <algorithm>
#include <vector>
#include <fstream>
#include <iostream>
#include <string>
std::ifstream in("");
std::ofstream out("outputfile.txt");
std::vector<int> numbers;
std::string sortType = "";
std::string file = "";
int main()
{
std::cout << "Which type of sort would you like to perform(sort or mergesort)?\n";
std::cin >> sortType;
std::cout << "Which file would you like to sort?\n";
std::cin >> file;
//Check if file exists
if(!in)
{
std::cout << std::endl << "The File is corrupt or does not exist! ";
return 1;
}
// Read all the ints from in:
copy(std::istream_iterator<int>(in), std::istream_iterator<int>(),
std::back_inserter(numbers));
//check if the file has values
if(numbers.empty())
{
std::cout << std::endl << "The file provided is empty!";
return 1;
} else
{
if(file == "sort")
{
sort(numbers);
}else
{
mergeSort();
}
}
}
void sort(std::vector<int>)
{
// Sort the vector:
sort(numbers.begin(), numbers.end());
unique(numbers.begin(), numbers.end());
// Print the vector with tab separators:
copy(numbers.begin(), numbers.end(),
std::ostream_iterator<int>(std::cout, "\t"));
std::cout << std::endl;
// Write the vector to a text file
copy(numbers.begin(), numbers.end(),
std::ostream_iterator<int>(out, "\t"));
std::cout << std::endl;
}
void mergeSort()
{
//mergesort code..
}

Answer 1

You need to declare the sort function before you call it. Move its definition above main, or put void sort(std::vector<int>); before main.
And the same goes for mergeSort.
You should also fully qualify the call sort(numbers.begin(), numbers.end()); as std::sort(numbers.begin(), numbers.end());, and the same for copy, unique. If you don't, then for technical reasons called "ADL", which you can look up if you like, then the call only compiles if the arguments that you're calling it on (the iterators) are classes in namespace std. It's up to the specific implementation whether or not they are, so the call won't work on some compilers.

Answer 2

I agree with #steve on declaring sort function before main().
I think the problem here is that you're calling the sort() function with parameter std::vector but in definition of the function you just wrote the type of received parameter, you should also write some name for the variable. eg.
void sort(std::vector<int> <variable_name>)
{
//definition
}
One more thing I want to point out is that as you have declared the vector number globally then there is no need to call the like sort(number), because function will automatically find the globally defined vector number. So basically if you want the vector number to be defined globally then the function sort() should be parameterless.
you have also used scope std:: everywhere, instead you can just add one line right after the #includes -
using namespace std;
I hope it works!