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stl map中的lower_bound和 upper_bound
阅读量:5056 次
发布时间:2019-06-12

本文共 3458 字,大约阅读时间需要 11 分钟。

map中的lower_bound和upper_bound的意思其实很简单,就两句话:

map::lower_bound(key):返回map中第一个大于或等于key的迭代器指针

map::upper_bound(key):返回map中第一个大于key的迭代器指针

所以,理解这两个函数请不要按照字面意义思考太复杂,因为仅仅是不小于(lower_bound)和大于(upper_bound)这么简单。

 

看两个msdn里的例子

1 // map_upper_bound.cpp 2 // compile with: /EHsc 3 #include  4 #include 
5 6 int main( ) 7 { 8 using namespace std; 9 map
m1;10 map
:: const_iterator m1_AcIter, m1_RcIter;11 typedef pair
Int_Pair;12 13 m1.insert ( Int_Pair ( 1, 10 ) );14 m1.insert ( Int_Pair ( 2, 20 ) );15 m1.insert ( Int_Pair ( 3, 30 ) );16  17  // 返回m1中第一个key值大于2的元素的迭代器,当然是<3,30>18  m1_RcIter = m1.upper_bound( 2 );19 cout << "The first element of map m1 with a key "20 << "greater than 2 is: "21 << m1_RcIter -> second << "." << endl;22 23 // If no match is found for the key, end is returned24 m1_RcIter = m1. upper_bound ( 4 );25 26 // m1中key值并没有大于或等于4的 27 if ( m1_RcIter == m1.end( ) )28 cout << "The map m1 doesn't have an element "29 << "with a key greater than 4." << endl;30 else31 cout << "The element of map m1 with a key > 4 is: "32 << m1_RcIter -> second << "." << endl;33 34 // The element at a specific location in the map can be found 35 // using a dereferenced iterator addressing the location36 m1_AcIter = m1.begin( );37 m1_RcIter = m1. upper_bound ( m1_AcIter -> first );38 cout << "The 1st element of m1 with a key greater than\n"39 << "that of the initial element of m1 is: "40 << m1_RcIter -> second << "." << endl;41 }

 

The first element of map m1 with a key greater than 2 is: 30.The map m1 doesn't have an element with a key greater than 4.The 1st element of m1 with a key greater thanthat of the initial element of m1 is: 20.
1 // map_lower_bound.cpp 2 // compile with: /EHsc 3 #include  4 #include 
5 6 int main( ) 7 { 8 using namespace std; 9 map
m1;10 map
:: const_iterator m1_AcIter, m1_RcIter;11 typedef pair
Int_Pair;12 13 m1.insert ( Int_Pair ( 1, 10 ) );14 m1.insert ( Int_Pair ( 2, 20 ) );15 m1.insert ( Int_Pair ( 3, 30 ) );16   //key值大于等于2的是<2,20>17 m1_RcIter = m1.lower_bound( 2 );18 cout << "The first element of map m1 with a key of 2 is: "19 << m1_RcIter -> second << "." << endl;20 21 // If no match is found for this key, end( ) is returned22 m1_RcIter = m1. lower_bound ( 4 );23 24 if ( m1_RcIter == m1.end( ) )25 cout << "The map m1 doesn't have an element "26 << "with a key of 4." << endl;27 else28 cout << "The element of map m1 with a key of 4 is: "29 << m1_RcIter -> second << "." << endl;30 31 // The element at a specific location in the map can be found 32 // using a dereferenced iterator addressing the location33 m1_AcIter = m1.end( );34 m1_AcIter--;35 m1_RcIter = m1. lower_bound ( m1_AcIter -> first );36 cout << "The element of m1 with a key matching "37 << "that of the last element is: "38 << m1_RcIter -> second << "." << endl;39 }

 

The first element of map m1 with a key of 2 is: 20.

The map m1 doesn't have an element with a key of 4.

The element of m1 with a key matching that of the last element is: 30.

转载于:https://www.cnblogs.com/fnlingnzb-learner/p/6097535.html

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