**How can you use function objects to achieve the functionality of built-in operators in C ?**

Getting Function Pointers to Built-in Operators

Operator Pointer Restrictions

In C , built-in operators lack true function pointer counterparts and do not play a role beyond overload resolution. To address this, the standard defines function objects that mirror the behavior of built-in operators.

Function Objects for Arithmetic and Comparison

The standard provides function objects to encapsulate arithmetic and comparison operations, such as:

• equal_to
• not_equal_to
• greater, less
• greater_equal
• less_equal

These objects provide equivalent functionality to their corresponding operators and can be used as function pointer arguments.

Standard Library Class Operators

Certain standard library operators allow for function pointers. However, this requires specifying the template type of the objects involved. For instance, to use the operator from std::basic_string, one could implement the following:

<code class="cpp">template<class Test>
Test test_function (Test const &amp;a, Test const &amp;b, Test (*FPtr)(Test const &amp;, Test const &amp;))
{
   return FPtr(a, b);
}</code>

Implementation Example

The following code demonstrates the usage of a function object for a comparison operation:

<code class="cpp">template<typename ParamsType, typename FnCompareType>
class MyAction
{
  public:
    MyAction(ParamsType& arg0, ParamsType& arg1, FnCompareType& fnCompare) 
    : arg0_(arg0), arg1_(arg1), fnCompare_(fnCompare) {}

    bool operator()()
    {
        if((*fnCompare_)(arg0_,arg1_))
        {
            // do this
        }
        else
        {
            // do s.th. else
        }
    }

  private:
    ParamsType& arg0_;
    ParamsType& arg1_;
    FnCompareType& fnCompare_;
};

void doConditional(int param1, int param2)
{
    MyAction<int, std::equal_to<int>> action(param1,param2);
    if(action())
    {
        // Do this
    }
    else
    {
        // Do that
    }
}</code>

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