I've got a list of elements, say, integers and I want to check if my variable (another integer) is one of the elements from the list. In python I'd do:
my_list = [1,2,3,4] # elements
my_var = 3 # my variable
my_var in my_list # returns boolean
How to do that in C++? I thought of using std::list, but I can find no find method in it. I can see such method in std::set structure.
More deeply, the problem is that my program is given some unique ids (a list, a set, whatever) and I iterate over a long list of input data (ids) and check if they are included in the list (boolean value returned for each iteration step). And I'm not sure how should I do that in C++.
you must #include <algorithm>, then you can use std::find
They really should add a wrapper. Like this:
namespace std
{
template<class _container,
class _Ty> inline
bool contains(_container _C, const _Ty& _Val)
{return std::find(_C.begin(), _C.end(), _Val) != _C.end(); }
};
...
if( std::contains(my_container, what_to_find) )
{
}
std::list does not provide a search method. You can iterate over the list and check if the element exists or use std::find. But I think for your situation std::set is more preferable. The former will take O(n) time but later will take O(lg(n)) time to search.
You can simply use:
int my_var = 3;
std::set<int> mySet {1, 2, 3, 4};
if(mySet.find(myVar) != mySet.end()){
//do whatever
}
Use std::find, something like:
if (std::find(std::begin(my_list), std::end(my_list), my_var) != std::end(my_list))
// my_list has my_var
A one-liner solution, similar to python, would be (std::set<int> {1, 2, 3, 4}).count(my_var) > 0.
Minimal working example
int my_var = 3;
bool myVarIn = (std::set<int> {1, 2, 3, 4}).count(my_var) > 0;
std::cout << std::boolalpha << myVarIn << std::endl;
prints true or false dependent of the value of my_var.
Declare additional helper function like this:
template <class T, class I >
bool vectorContains(const vector<T>& v, I& t)
{
bool found = (std::find(v.begin(), v.end(), t) != v.end());
return found;
}
And use it like this:
void Project::AddPlatform(const char* platform)
{
if (!vectorContains(platforms, platform))
platforms.push_back(platform);
}
Snapshot of example can be found here:
Source: Stackoverflow.com