C++ STL The compare function

The Compare Function in STL of C++

There are many comparing functions used in the STL.

There are 3 ways to implement the comparing function.

1. Using operation overloading to define <

1.1 Using own bool function

Define the element in STL like following:

struct T{    bool operator< (T other) const{        return weight < other.weight;    }    int index;    int weight;};

NOTE: cannot missing const!

1.2 Using friend function

Define the element in STL like following:

struct T{    friend bool operator< (T a, T b){        return a.weight < b.weight;    }    int index;    int weight;};

2. Using operator overloading to define ()

Using struct to reload ():

struct cmp{    bool operator () (T a, T b){        return a.weight < b.weight;    }};

And make it as a parameter in STL algorithm.

sort(container.begin(), container.end(), cmp());

NOTE: cannot miss the latest ()

3. Directly using bool function without struct:

bool cmp(T a, T b) {    return a.weight > b.weight;}sort(contain.begin(), container.end(), cmp);

NOTE: < is from little to large

    > is from large to little

4. Some intern comparing functions in the head file of functional

include <functional>

equal_to<Type>not_equal_to<Type> greater<Type>greater_equal<Type> less<Type>less_equal<Type>

Note: must add () when use

sort(begin, end, less<T>());