The 21st - -- the 30th time

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Lowercase letters are larger than uppercase letters , The letters after the alphabet are larger than the letters before

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map Is to save key value pairs ,map Duplicate keys are not allowed for , and multimap Allow key repetition

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set The data in will be sorted automatically

set Data duplication is not allowed ,multiset There can be duplicate data

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A function object is an object , But it works like a function

Function adapters can combine different function objects , Then pass it to the algorithm

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In the red box of the following figure is the function object , Express set The data in is sorted from small to large

Use functions for algorithms （ The figure below 1 Sum graph 2）

Use function objects for algorithms , Note that the member function in the function object must be called “operator”

Advantages of function objects over functions ： Function object is an intelligent function , And it has its own type , Function objects are generally faster than ordinary functions , And function objects can have their own state

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count_if and  count  Function the same , It's just count_if You can pass in functions or function pairs as predicates , If this function has only 1 Parameters , We call this predicate “ Unary predicate ”

The return value is bool Functions or function objects of type data are called “ The predicate ”

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The four algorithms in the above figure are applicable to all sequential containers and associated containers

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find() and  find_if()  These two algorithms are used for all containers , Be careful ,string It's a special container , And you can only use member functions  find()  Function to find , And string Of find（） The function returns not an iterator but a subscript

find() and  find_if()  Both algorithms are linear search , Slower

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