How to Safely Remove Elements from a Vector While Iterating in C ?

Removing Elements from a Vector Inside a Loop

While iterating through a vector using a for loop, a common task is to remove elements based on specific criteria. However, attempting to remove an element within the loop itself can lead to errors.

Consider the following code:

for (vector<Player>::iterator it = allPlayers.begin(); it != allPlayers.end(); it++)
{
    if(it->getpMoney() <= 0) 
        it = allPlayers.erase(it);
    else 
        ++it;
}

This code attempts to remove players with negative or zero money from the vector allPlayers. However, it results in the error message:

'operator =' function is unavailable in 'Player'

The Problem

The error arises because the erase() method internally utilizes the assignment operator = to move elements within the vector. To use erase(), the Player objects must be assignable, requiring an implementation of the operator= for the Player class.

The Solution

To resolve the issue, avoid incrementing it within the for loop:

for (vector<Player>::iterator it = allPlayers.begin(); it != allPlayers.end(); /*it++*/)
{
    if(it->getpMoney() <= 0) 
        it = allPlayers.erase(it);
}

Implement the operator= for the Player class to enable assigning objects within the vector.

Alternative Approach Using Algorithms

To simplify the code, consider using the Erase-Remove Idiom:

allPlayers.erase(
    std::remove_if(
        allPlayers.begin(), 
        allPlayers.end(),
        [](Player const &amp; p) { return p.getpMoney() <= 0; }
    ), 
    allPlayers.end()
); 

This code employs the std::remove_if() algorithm to filter out players with negative or zero money, and then uses erase() to remove them from the vector.

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