If I have
vector<T> list Where each element in the list is unique, what's the easiest way of deleting an element provided that I don't know if it's in the list or not? I don't know the index of the element and I don't care if it's not on the list.
You could use the Erase-remove idiom for std::vector
Quote:
std::vector<int> v; // fill it up somehow v.erase(std::remove(v.begin(), v.end(), 99), v.end()); // really remove all elements with value 99 Or, if you're sure, that it is unique, just iterate through the vector and erase the found element. Something like:
for( std::vector<T>::iterator iter = v.begin(); iter != v.end(); ++iter ) { if( *iter == VALUE ) { v.erase( iter ); break; } } 
iter is invalidated after .erase(), and ++iter would fail immediately. Would have to write iter=v.erase(iter); instead. Now if you do it that way, an extra ++iter will be committed after an erasure, skipping elements. To fix this you should always iterate backwards through the vector when deleting elements. Using a numerical index will fix these problems. for( int i = v.size()-1; i >= 0; i-- ) if( v[i]==VALUE ) v.erase( v.begin()+i ) ;
Based on Kiril's answer, you can use this function in your code :
template<typename T> inline void remove(vector<T> & v, const T & item) { v.erase(std::remove(v.begin(), v.end(), item), v.end()); } And use it like this
remove(myVector, anItem); If occurrences are unique, then you should be using std::set<T>, not std::vector<T>.
This has the added benefit of an erase member function, which does what you want.
See how using the correct container for the job provides you with more expressive tools?
#include <set> #include <iostream> int main() { std::set<int> notAList{1,2,3,4,5}; for (auto el : notAList) std::cout << el << ' '; std::cout << '\n'; notAList.erase(4); for (auto el : notAList) std::cout << el << ' '; std::cout << '\n'; } // 1 2 3 4 5 // 1 2 3 5 
If occurrences are unique, then you should be using std::set<T>, not std::vector<T> is nowhere valid. Let's just focus on the OP's settings.From c++20
//LIKE YOU MENTIONED EACH ELEMENT IS UNIQUE std::vector<int> v = { 2,4,6,8,10 }; //C++20 UNIFORM ERASE FUNCTION (REMOVE_ERASE IDIOM IN ONE FUNCTION) std::erase(v, 8); //REMOVES 8 FROM VECTOR Now try
std::erase(v, 12); Nothing will happen, the vector remains intact.
vectorcontainer islist.. It could be confusing, a lot (for someone, that reads your code)vectoris. And both are pretty different :)