[C++] Study Notes: 21 Days to Learn C++ Chapter 15-22 Highlights

STL sequential containers

std::vector std::deque
std::list 
std::forward_list

STL associative containers

std::set std::unordered_set 
std::map std::unordered_map 
std::multiset std::unordered_multiset
std::multimap std::unordered_multimap

STL container adapter

std::stack std::queue std::priority_queue

STL string class

std::string std::wstring

for(auto charLocator = stlString.cbegin();charLocator !=stlString.end();++charLocator){}

std::string lookup

while(subStr!=string::npos)
{
// Make find() search forward from the next character onwards
size_t searchOffset = subStrPos + 1;
subStrPos = sampleStr.find(“ ”,searchOffset);
}

std::string reverse

reverse(sampleStr.begin(),sampleStr.end());

case conversion

transform(inStr.begin().inStr.end(),inStr.begin(),::toupper);
transform(inStr.begin().inStr.end(),inStr.begin(),::tolower);

oprator "" s for C++14 std::string

Use pointer syntax to access elements in vector

vector<int>::const_iterator element =   integers.cbegin();
auto  element = integers.cbegin();

std::vector size vec.size(); capacity vec.capacity(); allocation capacity vec.reserve(num);
std::deque is similar to vector, but supports push_front() and pop_front()
std::list inversion list.reverse() Sort list.sort()
std::forward_list When inserting elements, only push_front() can be used, and insert() can also be used to insert

STL set and multiset specify sorting criteria

// used as a template parameter in set / multiset instantiation
template <typename T>
struct SortDescending
{
	bool operator()(const T& lhs, const T& rhs) const
	{
	 return (lhs>rhs);
	}
}
set <int, SortDescending<int>> setInts;
multisets <int, SortDescending<int>> msetInts;

Tips：对于其对象储存在set或multiset等容器中的类，别忘了在其中实现运算符<和==，分别用于排序和查找。

STL std::map and std::multimap instantiation

#include <map>
using namespace std;
...
map<keyType, valueType, Predicate = std::less<keyType>> mapObj;
multimap <keyType, valueType, Predicate = std::less<keyType>> mmapObj;

insert element

insert(make_pair(key, value));
insert(pair<keyType, valueType>(key, value));

Find elements in multimap

auto pairFound = mmapIntToStr.find(key);

// check if find() succeeded;
if(pairFound != mmapIntToStr.end())
{
	// Find the number of pairs that have the same supplied key
	size_t numPairInMap = mmapIntToStr.count(key);

	for(size_t count = 0 ;count < numPairInMap;++count)
	{
	cout << “Key:” << pairFound->first ;
	cout << “, Value [” << counter << “] = ”;
	cout << pairFound->second << endl;
	
	++ pairFound;
	}
}
else
	cout << “Element not found in the multimap”;

基于散列表的STL键值对容器std::unordered_map, 其平均插入和删除时间固定，查找元素的时间也是固定的。

散列函数hash_function();load_factor()指出了unordered_map桶的填满程度。因插入元素导致load_factor()超过max_load_factor()时，unordered_map将重新组织以增加桶数，并重建散列表。

Function object to store state

template<typename elementType>
struct DisplayElementKeepCount
{
	int count;
	DisplayElementKeepCount():count(0) {}
	void operator()(const elementType& elelment)
	{
	++count;
	cout << element << ‘ ’;
	}
};

General syntax for lambda expressions

[stateVar1, stateVar2](Type1& var1, Type2& var2){// lambda code here;}

To modify a state variable in a lambda expression

[stateVar1, stateVar2](Type& param) mutable {// lambda code here;}

If the modification is still valid externally

[&stateVar1, &stateVar2](Type& param) {// lambda code here;}

To explicitly specify the return type

[stateVar1, stateVar2](Type var1, Type var2) -> ReturnType
{return (value or expression);}

In the case of compound statements

[stateVar1, stateVar2](Type var1, Type var2) -> ReturnType
{
	Statement 1;
	Statement 2;
	return (value or expression);
}

To pass all local variables

[=](Type& Param, ...){... expression;}

A lambda expression instance that accepts a state variable via a capture list

[divisor](int dividend){return (dividend%divisor) == 0;}

[C++] Study Notes: 21 Days to Learn C++ Chapter 15-22 Highlights

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