I was wondering if there's any built-in or well-established way (i.e. via lambda) to go through the elements of an std::list and find all the ones that match a given value? I know I can iterate through all of them, but I thought I'd ask if there's a way to get an iterator that iterates through just the elements that match a given criteria? My sample below only gives me the iterator to the first matching element.
#include <list>
#include <algorithm>
#include <stdio.h>
int main()
{
std::list<int> List;
List.push_back(100);
List.push_back(200);
List.push_back(300);
List.push_back(100);
int findValue = 100;
auto it = std::find_if(List.begin(), List.end(), [findValue](const int value)
{
return (value == findValue);
});
if (it != List.end())
{
for (; it != List.end(); ++it)
{
printf("%d\n", * it);
}
}
return 0;
}
Thanks for any feedback.
std::find_if
is a generalisation of std::find
for when you need a function to check for the elements you want, rather than a simple test for equality. If you just want to do a simple test for equality then there's no need for the generalised form, and the lambda just adds complexity and verbosity. Just use std::find(begin, end, findValue)
instead:
std::vector<std::list<int>::const_iterator> matches;
auto i = list.begin(), end = list.end();
while (i != end)
{
i = std::find(i, end, findValue);
if (i != end)
matches.push_back(i++);
}
But rather than calling find
in a loop I'd just write the loop manually:
std::vector<std::list<int>::const_iterator> matches;
for (auto i = list.begin(), toofar = list.end(); i != toofar; ++i)
if (*i == findValue)
matches.push_back(i);