How to Search Vectors of Structs Based on Internal Properties: A Guide to std::find_if

Searching Vectors of Structs with std::find

When working with vectors of complex data structures like structs, the built-in std::find function becomes insufficient if you need to search for specific elements based on their internal properties. Using a simple example, we'll explore how to overcome this limitation.

Consider the following struct:

<code class="cpp">struct monster { 
    DWORD id;
    int x;
    int y;
    int distance;
    int HP;
};</code>

Now, let's say you have a vector of these monsters named bot.monsters. To search for a monster with a specific ID, we could use std::find, but since the ID is a member of the monster struct, we need to tell the function how to access it.

The std::find_if function provides a way to specify a custom criteria. We can define a lambda function that extracts the ID from each monster and compares it to our target ID:

<code class="cpp">it = std::find_if(bot.monsters.begin(), bot.monsters.end(), 
        boost::bind(&monster::id, _1) == currentMonster);</code>

This lambda function effectively filters the vector, iterating through each monster and returning true if its ID matches the specified currentMonster ID.

If you don't have access to the Boost library, you can write your own function object:

<code class="cpp">struct find_id : std::unary_function<monster, bool> {
    DWORD id;
    find_id(DWORD id):id(id) { }
    bool operator()(monster const& m) const {
        return m.id == id;
    }
};

it = std::find_if(bot.monsters.begin(), bot.monsters.end(), 
         find_id(currentMonster));</code>

This custom function object allows us to perform the same search, but without the need for Boost.

By using std::find_if and a custom criteria, we can effectively search through vectors of complex data structures based on their specific member values, providing greater flexibility in data manipulation.

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