C++ 学习小程序之　map 的用法

１．　map::at

1 #include

2 #include

3 #include

4 using namespace std;

5

6 int main(){

7 map mymap = {

8 {"alpha", 0},

9 {"beta", 0},

10 {"gamma", 0}};

11

12 mymap.at("alpha") = 10;

13 mymap.at("beta") = 20;

14 mymap.at("gamma") = 30;

15

16 for (auto& x:mymap){

17 cout<

18 }

19

20 return 0;

21 }

２．　make_pair example

1 // make_pair example

2 #include // std::pair

3 #include // std::cout

4

5 int main () {

6 std::pair foo;

7 std::pair bar;

8

9 foo = std::make_pair (10,20);

10 bar = std::make_pair (10.5,'A'); // ok: implicit conversion from pair

11

12 std::cout << "foo: " << foo.first << ", " << foo.second << '\n';

13 std::cout << "bar: " << bar.first << ", " << bar.second << '\n';

14

15 return 0;

16 }

３．　map::begin/end

1 // map::begin/end

2 #include

3 #include

4

5 int main ()

6 {

7 std::map mymap;

8

9 mymap['b'] = 100;

10 mymap['a'] = 200;

11 mymap['c'] = 300;

12

13 // show content:

14 for (std::map::iterator it=mymap.begin(); it!=mymap.end(); ++it)

15 std::cout << it->first << " => " << it->second << '\n';

16

17 return 0;

18 }

4.   map::insert(C++98)

1 // map::insert(C++98)

2 #include

3 #include

4 using namespace std;

5 int main ()

6 {

7 map mymap;

8

9 // first insert function version (single parameter):

10 mymap.insert ( pair('a', 100) );

11 mymap.insert ( pair('z', 200) );

12

13 pair::iterator, bool> ret;

14 ret = mymap.insert (pair('z',500));

15 if (ret.second == false){

16 cout<<"element 'z' already existed";

17 cout<<"with a value of " << ret.first->second << '\n';

18 }

19

20 //second insert function version (with hint position):

21 map::iterator it = mymap.begin();

22 mymap.insert (it, pair('b',300)); // max efficiency inserting

23 mymap.insert (it, pair('c',400)); // no max efficiency inserting

24

25 //third insert function version (range insertion):

26 map anothermap;

27 anothermap.insert(mymap.begin(),mymap.find('c'));

28

29 // showing contents:

30 cout<<"mymap contains: \n";

31 for (it = mymap.begin(); it!= mymap.end(); ++it)

32 cout<first<<"=>"<second<<'\n';

33

34 cout<<"anothermap contains: \n";

35 for(it=anothermap.begin(); it!=anothermap.end();++it)

36 cout<first<<"=>"<second<<'\n';

37

38 return 0;

39 }

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