Variables not declared in this scope - c++

Question

The problem lies within the block:
check_sort(l.begin(), l.end(), "list");
time_insert(insert_list, data);
check_sort(s.begin(), s.end(), "set");
time_insert(insert_set, data);
check_sort(v.begin(), v.end(), "vector");
time_insert(insert_vector, data);
The error states that the variables are not declared in the scope, but shouldn't l,s,v be universal variables here? What am I doing wrong.
#include <cmath>
#include <iterator>
#include <iostream>
#include <iomanip>
#include <vector>
#include <ctime>
#include <list>
#include <set>
#include <algorithm>
#include <cstdlib>
using namespace std;
typedef void Inserter(vector<double>);
vector<double> gen_data(int num_elts);
void insert_list(vector<double> data);
void insert_set(vector<double> data);
void insert_vector(vector<double> data);
void time_insert( Inserter inserter, vector<double> data);
template <class Iter> bool is_sorted(Iter first, Iter last);
template <class Iter> void check_sort(Iter first, Iter last, string cont_kind);
int main() {
srand(time(0));// initialize random number generator
cout << "How many elements for container? ";
int num_elts = 0;
while (cin >> num_elts) {
if (num_elts <= 0)
cout << "Error, should be > 1";
else {
vector<double> data = gen_data(num_elts);
check_sort(l.begin(), l.end(), "list");
time_insert(insert_list, data);
check_sort(s.begin(), s.end(), "set");
time_insert(insert_set, data);
check_sort(v.begin(), v.end(), "vector");
time_insert(insert_vector, data);
}
cout << "\nHow many elements for next container? ";
}
return 0;
}
void time_insert( Inserter inserter, vector<double> data) {
clock_t t1 = clock();
if (t1 == clock_t(-1)) { //if clock() doesn’t work
cerr << "sorry, no clock\n";
exit(1);
}
inserter(data);
clock_t t2 = clock();
if (t2 == clock_t(-1)) {
cerr << "sorry, clock overflow\n";
exit(2);
}
cout << "Elapsed time: " << fixed << setprecision(2)
<< double(t2-t1)/CLOCKS_PER_SEC << " seconds\n";
}
class Larger_than {
double v;
public:
Larger_than(double vv) : v(vv){}
bool operator()(double x) const {return x>v;}
};
// Sorts and then inserts data into a list
void insert_list(vector<double> data)
{
list<double> l;
for(int i=0; i < data.size(); i++){
list<double>::iterator p = find_if(l.begin(),l.end(), Larger_than(data[i]));
l.insert(p, data[i]);
}
}
// Sorts and then inserts data into a list
void insert_set(vector<double> data)
{
set<double> s;
for(int i=0; i < data.size(); i++){
set<double>::iterator p = find_if(s.begin(),s.end(), Larger_than(data[i]
));
s.insert(p, data[i]);
}
}
// Sorts and then inserts data into a list
void insert_vector(vector<double> data)
{
vector<double> v;
for(int i=0; i < data.size(); i++){
vector<double>::iterator p = find_if(v.begin(),v.end(), Larger_than(data
[i]));
v.insert(p, data[i]);
}
}
// generate num_elts random numbers in the range [0.0, 1.0),
// which are returned in a vector
vector<double> gen_data (int num_elts)
{
vector<double> result;
for (int i = 0; i < num_elts; i++) {
double datum = 1.0*rand()/RAND_MAX;
result.push_back(datum);
}
return result;
}
// is container spanned by [from, last) sorted?
template <class Iter> bool is_sorted(Iter first, Iter last)
{
Iter next = first; // next element
for (next++; next != last; next++, first++) {
if (*first > *next)
return false;
}
return true;
}
// prints a msg describing container kind, as well as whether container
// spanned by [from, last) is sorted
template <class Iter> void check_sort(Iter first, Iter last, string cont_kind)
{
cout << "Check: " << cont_kind << " is ";
if (!is_sorted(first, last)) cout << "not ";
cout << "sorted\n";
}

Answer 1

How should main know about s, l and v at all? They're local variables of completely unrelated functions (the insert_xxx ones), there's no way main could know about them. If you want to make them globally accessible, just make them global variables, i.e., put their definition before main:
// ...
list<double> l;
set<double> s;
vector<double> v;
int main(){
// ....
}
// ...

Answer 2

It looks like l is defined in the 'insert_list' function and would not available in main. Only variables defined insider your function are available.

Answer 3

You don't appear to have declared the variables at all. Why do you think they should exist in main? There are no globals or locals with those names anywhere that I can see. Try declaring them before using them.