C++ language’s standard vector has a function called “find_if” provides search functionality depends on a boolean return typed function. Let’s say you have an integer vector and trying to find an even number :
#include <iostream>
#include <algorithm>
#include <vector>
bool IsEven (int i) {
return ((i%2)==0);
}
int main () {
std::vector<int> numberVector;
numberVector.push_back(1);
numberVector.push_back(3);
numberVector.push_back(5);
numberVector.push_back(6);
numberVector.push_back(7);
std::vector<int>::iterator it = std::find_if (numberVector.begin(), numberVector.end(), IsEven);
printf("First even number : %d", *it);
return 0;
}But what if you want to pass an additional parameter to your search function and use lambda functions. Take a look to the following code snippet. We have a Popup object and a lambda function defines a search condition depending on name of the popup.
#include <iostream>
#include <algorithm>
#include <vector>
#include <functional>
#include "Popup.h"
int main () {
std::vector<Popup*> popups;
popups.push_back(new Popup("name1", "message1"));
popups.push_back(new Popup("name2", "message2"));
popups.push_back(new Popup("name3", "message3"));
const char* popupName = "name2";
std::vector<Popup*>::iterator it = std::find_if(popups.begin(), popups.end(), [popupName](Popup* popup)->bool {
return strcmp(popup->getName(), popupName) == 0;
});
return 0;
}It is so simple, lambda function’s scope holds the local constant “popupName”. Finally iterator “it” holds the result :)