该文档举例说明了multimap的查找和删除元素的使用
该文档举例说明了multimap的查找和删除元素的使用。
其中,在使用迭代器遍历元素的时候,如果使用了删除迭代器的操作,那么需要小心迭代器失效的情况。
- /*
- 功能说明:
- multimap的查找和删除元素的使用举例
- 代码说明:
- 使用multimap的equal_range()方法来查找符合指定key的元素。使用erase来删除指定key的元素。
- 实现方式:
- 限制条件或者存在的问题:
- 无
- */
- #include <iostream>
- #include <string>
- #include <map>
- using namespace std;
- class CData
- {
- public:
- CData()
- {
- sequence = ;
- this->remark = "default string";
- cout << "CData()\t" << toString() << "\t" << endl;
- }
- CData(int i, string &s)
- {
- this->sequence = i;
- this->remark = s;
- cout << "CData(int i,string &s)\t" << toString() << "\t" << endl;
- }
- CData(const CData &data)
- {
- this->sequence = data.sequence;
- this->remark = data.remark;
- cout << "CData(const CData &data)\t" << toString() << "\t" << endl;
- }
- CData operator = (const CData &data)
- {
- this->sequence = data.sequence;
- this->remark = data.remark;
- cout << "CData operator = (const CData &data)\t" << toString() << "\t" << endl;
- return *this;
- }
- void setSequence(const int i)
- {
- this->sequence = i;
- }
- void setRemark(const string &s)
- {
- this->remark = s;
- }
- string toString() const
- {
- char tmp[] = { };
- sprintf(tmp, "[sequence:%d | remark:%s @ %p]", this->sequence, this->remark.c_str(),this);
- //此处应该有内存复制操作,所以不用担心返回后tmp数组所指向的内存被修改或者不存在的情况。
- return tmp;
- }
- ~CData()
- {
- cout << "~CData()\t" << this << endl;
- }
- protected:
- private:
- int sequence;
- string remark;
- };
- int main(int argc, char ** argv)
- {
- cout << "process begin @[" << (void*)&main << "]" << endl;
- multimap<string, CData *> multData;
- string strClassName = "CData11";
- CData *p11 = new CData(, strClassName);
- strClassName = "CData12";
- CData *p12 = new CData(, strClassName);
- strClassName = "CData13";
- CData *p13 = new CData(, strClassName);
- strClassName = "CData23";
- CData *p23 = new CData(, strClassName);
- strClassName = "CData24";
- CData *p24 = new CData(, strClassName);
- strClassName = "CData26";
- CData *p26 = new CData(, strClassName);
- multData.insert(make_pair("", p11));
- multData.insert(make_pair("", p23));
- multData.insert(make_pair("", p13));
- multData.insert(make_pair("", p24));
- multData.insert(make_pair("", p12));
- multData.insert(make_pair("", p26));
- cout << "multData.size()\t" << multData.size() << endl;
- cout << "show all msg" << endl;
- // multimap在创建的时候,已经将元素根据key的顺序排好了(前提是key支持<比较)。
- for (multimap<string, CData*>::iterator itr = multData.begin(); itr != multData.end(); itr++)
- {
- cout << itr->first << "\t" << (itr->second)->toString() << endl;
- }
- cout << "find 2" << endl;
- pair<multimap<string, CData*>::iterator, multimap<string, CData*>::iterator> pitr2 = multData.equal_range("");
- for (multimap<string, CData*>::iterator itr = pitr2.first; itr != pitr2.second; itr++)
- {
- cout << itr->first << "\t" << (itr->second)->toString() << endl;
- }
- multData.erase("");
- pitr2 = multData.equal_range("");
- if (pitr2.first == pitr2.second)
- {
- cout << "can not find key 2 after delete key 2" << endl;
- }
- cout << "show all msg after delete 2" << endl;
- for (multimap<string, CData*>::iterator itr = multData.begin(); itr != multData.end(); itr++)
- {
- cout << itr->first << "\t" << (itr->second)->toString() << endl;
- }
- multData.insert(make_pair("", p11));
- multData.insert(make_pair("", p23));
- multData.insert(make_pair("", p13));
- multData.insert(make_pair("", p24));
- multData.insert(make_pair("", p12));
- multData.insert(make_pair("", p26));
- cout << "find element by key using another way" << endl;
- for (multimap<string, CData*>::iterator itr_find = multData.lower_bound(""); itr_find != multData.upper_bound(""); itr_find++)
- {
- cout << itr_find->first << "\t" << (itr_find->second)->toString() << endl;
- }
- cout << "delete key 1 by iterator" << endl;
- // 这是一种错误的迭代器删除元素的方式。
- /*
- for (multimap<string, CData*>::iterator itr = multData.begin(); itr != multData.end(); itr++)
- {
- cout << itr->first << "\t" << (itr->second)->toString() << endl;
- if (itr->first == "1")
- {
- multData.erase(itr);
- }
- }
- */
- // 正确的使用迭代器删除元素的方式。
- for (multimap<string, CData*>::iterator itr = multData.begin(); itr != multData.end(); )
- {
- if (itr->first == "")
- {
- cout <<"find key 1. "<< itr->first << "\t" << (itr->second)->toString() << endl;
- itr = multData.erase(itr);
- }
- else
- {
- cout << "can not find key 1. " << itr->first << "\t" << (itr->second)->toString() << endl;
- itr++;
- }
- }
- cout << "show all msg after erase key 1" << endl;
- for (multimap<string, CData*>::iterator itr = multData.begin(); itr != multData.end(); itr++)
- {
- cout << itr->first << "\t" << (itr->second)->toString() << endl;
- }
- delete p11;
- delete p12;
- delete p13;
- delete p23;
- delete p24;
- delete p26;
- return ;
- }
程序的输出结果:
process begin @[00B2188E]
CData(int i,string &s) [sequence:11 | remark:CData11 @ 011FCFD0]
CData(int i,string &s) [sequence:12 | remark:CData12 @ 011FD020]
CData(int i,string &s) [sequence:13 | remark:CData13 @ 011FD8C0]
CData(int i,string &s) [sequence:23 | remark:CData23 @ 011FE448]
CData(int i,string &s) [sequence:24 | remark:CData24 @ 011FE6C8]
CData(int i,string &s) [sequence:26 | remark:CData26 @ 011FE808]
multData.size() 6
show all msg
1 [sequence:11 | remark:CData11 @ 011FCFD0]
1 [sequence:13 | remark:CData13 @ 011FD8C0]
1 [sequence:12 | remark:CData12 @ 011FD020]
2 [sequence:23 | remark:CData23 @ 011FE448]
2 [sequence:24 | remark:CData24 @ 011FE6C8]
2 [sequence:26 | remark:CData26 @ 011FE808]
find 2
2 [sequence:23 | remark:CData23 @ 011FE448]
2 [sequence:24 | remark:CData24 @ 011FE6C8]
2 [sequence:26 | remark:CData26 @ 011FE808]
can not find key 2 after delete key 2
show all msg after delete 2
1 [sequence:11 | remark:CData11 @ 011FCFD0]
1 [sequence:13 | remark:CData13 @ 011FD8C0]
1 [sequence:12 | remark:CData12 @ 011FD020]
find element by key using another way
1 [sequence:11 | remark:CData11 @ 011FCFD0]
1 [sequence:13 | remark:CData13 @ 011FD8C0]
1 [sequence:12 | remark:CData12 @ 011FD020]
1 [sequence:11 | remark:CData11 @ 011FCFD0]
1 [sequence:13 | remark:CData13 @ 011FD8C0]
1 [sequence:12 | remark:CData12 @ 011FD020]
delete key 1 by iterator
find key 1. 1 [sequence:11 | remark:CData11 @ 011FCFD0]
find key 1. 1 [sequence:13 | remark:CData13 @ 011FD8C0]
find key 1. 1 [sequence:12 | remark:CData12 @ 011FD020]
find key 1. 1 [sequence:11 | remark:CData11 @ 011FCFD0]
find key 1. 1 [sequence:13 | remark:CData13 @ 011FD8C0]
find key 1. 1 [sequence:12 | remark:CData12 @ 011FD020]
can not find key 1. 2 [sequence:23 | remark:CData23 @ 011FE448]
can not find key 1. 2 [sequence:24 | remark:CData24 @ 011FE6C8]
can not find key 1. 2 [sequence:26 | remark:CData26 @ 011FE808]
show all msg after erase key 1
2 [sequence:23 | remark:CData23 @ 011FE448]
2 [sequence:24 | remark:CData24 @ 011FE6C8]
2 [sequence:26 | remark:CData26 @ 011FE808]
~CData() 011FCFD0
~CData() 011FD020
~CData() 011FD8C0
~CData() 011FE448
~CData() 011FE6C8
~CData() 011FE808
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