CODEWITHSUNDEEP
c++c++11
Igor Karadzic
Igor Karadzic

Reputation: 45

Removing Struct object from list using remove method in C++

I am trying to use remove method from list on struct object to remove it. This is my struct:

typedef struct pair{
  int x;
  int y;
} PAIR;

And this is code where i use it and where the error occurs:

list<PAIR> openSet;
PAIR pair;
pair.x = xStart;
pair.y = yStart;
openSet.push_front(pair);

PAIR current;
for(PAIR p : openSet){
    if(fScores[p.x * dim + p.y] < maxVal){
         maxVal = fScores[p.x * dim + p.y];
         current = p;
    }
}

openSet.remove(current);

Error that i am getting is this:

 no match for ‘operator==’ (operand types are ‘pair’ and ‘const value_type’ {aka ‘const pair’})

Can you tell me how to fix this?

Upvotes: 0

Views: 80

Answers (1)

Remy Lebeau
Remy Lebeau

Reputation: 595582

To use std::list::remove(), elements have to be comparable for equality. Implement an operator== for your struct, eg:

typedef struct pair{
  int x;
  int y;

  bool operator==(const pair &rhs) const {
    return x == rhs.x && y == rhs.y;
  }
} PAIR;

Otherwise, use std::find_if() and std::list::erase():

auto iter = std::find_if(openSet.begin(), openSet.end(),
  [&](const PAIR &p){ return p.x == current.x && p.y == current.y; }
);
if (iter != openSet.end()) {
  openSet.erase(iter);
}

Or, std::list::remove_if():

openSet.remove_if(
  [&](const PAIR &p){ return p.x == current.x && p.y == current.y; }
);

Or, change your loop to use iterators explicitly:

list<PAIR>::iterator current = openSet.end();
for(auto iter = openSet.begin(); iter != openSet.end(); ++iter){
    PAIR &p = *iter;
    if (fScores[p.x * dim + p.y] < maxVal){
         maxVal = fScores[p.x * dim + p.y];
         current = iter;
    }
}

if (current != openSet.end()) {
    openSet.erase(current);
}

Upvotes: 5

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