I made a palindrome function that allows me to use any container type, and it worked for string, vector, and deque but when I made an STL list and tried running the code, but I get the error bellow and I couldn't figure out what that means and what to do.
Severity Code Description Project File Line Suppression State
Error C2676 binary '-': 'std::_List_const_iterator<std::_List_val<std::_List_simple_types<_Ty>>>' does not define this operator or a conversion to a type acceptable to the predefined operator homework4 C:\...\Source.cpp 9
Severity Code Description Project File Line Suppression State
Error C3536 'itr1': cannot be used before it is initialized homework4 C:\...\Source.cpp 9
Severity Code Description Project File Line Suppression State
Error C2676 binary '<': 'std::_List_const_iterator<std::_List_val<std::_List_simple_types<_Ty>>>' does not define this operator or a conversion to a type acceptable to the predefined operator homework4 C:\...\Source.cpp 9
Severity Code Description Project File Line Suppression State
Error C2100 illegal indirection homework4 C:\...\Source.cpp 10
Below the code I ran.
#include <iostream>
#include<list>
#include<vector>
#include<deque>
using namespace std;
template <typename Container>
bool palindrome(const Container& s) {
for (auto itr = s.begin(), itr1 = s.end() - 1; itr < itr1; itr++, itr1--) {
if (*itr != *itr1)
return false;
}
return true;
}
void main() {
const string word1{ "racecar" };
const vector<char> word2{ 'a', 'b', 'b', 'a' };
const deque<int> word3{ 83, 84, 65, 84, 83 };
const list<int> word4{ 83, 84, 65, 84, 83 };
word4.end();
cout << palindrome< string >(word1) << endl;
cout << palindrome< vector<char> >(word2) << endl;
cout << palindrome< deque<int> >(word3) << endl;
cout << palindrome< list<int> >(word4) << endl;
}
The standard container std::list has bidirectional iterators. The operator - used in this expression
itr1 = s.end() - 1
is defined for random access iterators. You could use instead the standard function std::prev declared in the header <iterator> like
itr1 = std::prev( s.end() )
However in any case the function is invalid because in general the user of the function can pass an empty container. In this case the expression std::prev( s.end() ) has undefined behavior.
And the operator < is not defined for bidirectional iterators. So this expression
itr < itr1
also may not be used in the function.
Moreover the function will not work with arrays because arrays do not have member functions like for example begin().
The function can look the following way as it is shown in the demonstrative program below.
#include <iostream>
#include <iomanip>
#include <string>
#include <deque>
#include <vector>
#include <list>
#include <iterator>
template <typename Container>
bool palindrome( const Container &c )
{
auto first = std::begin( c );
auto last = std::end( c );
while ( first != last && first != --last && *first == *last ) ++first;
return first == last;
}
int main()
{
const std::string word1{ "racecar" };
const std::vector<char> word2{ 'a', 'b', 'b', 'a' };
const std::deque<int> word3{ 83, 84, 65, 84, 83 };
const std::list<int> word4{ 83, 84, 65, 84, 83 };
const char word5[] = { 83, 84, 65, 84, 83 };
std::cout << std::boolalpha << palindrome( word1 ) << '\n';
std::cout << std::boolalpha << palindrome( word2 ) << '\n';
std::cout << std::boolalpha << palindrome( word3 ) << '\n';
std::cout << std::boolalpha << palindrome( word4 ) << '\n';
std::cout << std::boolalpha << palindrome( word5 ) << '\n';
return 0;
}
The program output is
true
true
true
true
true
If you want you can specialize the function for random access iterators.