在map中保存struct，及map的文件输入输出

迈不过友情╰ 2024-02-17 22:36 5阅读 0赞

自己写的代码，因为我记忆力差的惊人，所以一方面以后我用到这个代码直接复制粘贴反正会忘，就不费力记了。另一方面，看到国内很多这样现成的例子少，所以方便大家。

用函数的方法实现：

从map输出到文件，map的value是struct

\#include<map>  
\#include<iostream>  
\#include<string>  
\#include<fstream>  
using namespace std;

struct studentID \{  
string name;  
string address;  
\};

studentID MakeStudentID(const string name, const string address)  
\{  
studentID c=\{name, address\};  
return c;  
\}

int main()  
\{  
int number\[2\]=\{49,21\};  
map<int, studentID> studentID\_table;  
studentID\_table.insert(make\_pair(number\[0\],MakeStudentID("Tom","Dalian")));  
studentID\_table.insert(make\_pair(number\[1\],MakeStudentID("Lee","Shenyangi")));  
ofstream outFile("newfile.txt");  
map<int, studentID>::const\_iterator map\_it = studentID\_table.begin();  
while(map\_it!= studentID\_table.end())  
\{  
outFile << map\_it->first<<endl;  
outFile << map\_it->second.name<<endl;  
outFile << map\_it->second.address<<endl;  
map\_it++;  
\}  
return 0;  
outFile.close();  
\}

用构造constructor的方法：

\#include<map>  
\#include<iostream>  
\#include<string>  
\#include<fstream>  
using namespace std;

struct studentID \{  
studentID(): name(),address() \{\}  
studentID(string newname, string newaddress): name(newname), address(newaddress) \{\}  
string name;  
string address;  
\};

int main()  
\{  
int number\[2\]=\{49,21\};  
map<int, studentID> studentID\_table;  
studentID\_table.insert(make\_pair(number\[0\],studentID("Tom","Dalian")));  
studentID\_table.insert(make\_pair(number\[1\],studentID("Lee","Shenyangi")));  
ofstream outFile("newfile.txt");  
map<int, studentID>::const\_iterator map\_it = studentID\_table.begin();  
while(map\_it!= studentID\_table.end())  
\{  
outFile << map\_it->first<<endl;  
outFile << map\_it->second.name<<endl;  
outFile << map\_it->second.address<<endl;  
map\_it++;  
\}  
return 0;  
outFile.close();  
\}

其中关于向map中插入值一段：

int number\[2\]=\{49,21\};  
map<int, studentID> studentID\_table;  
studentID\_table.insert(make\_pair(number\[0\],studentID("Tom","Dalian")));  
studentID\_table.insert(make\_pair(number\[1\],studentID("Lee","Shenyangi")));

等价于：

map<int, studentID> studentID\_table;  
studentID\_table\[49\]=studentID("Tom","Dalian");  
studentID\_table\[21\]=studentID("Lee","Shenyangi");

输出结果如下

\-bash-4.1$ more newfile.txt  
21  
Lee  
Shenyangi  
49  
Tom  
Dalian

不管创建map时哪个学号先创建，顺序输出时永远是按照key值由小到大排列的，这是map数据结构本身的优点

从文件输入：

\#include<map>  
\#include<iostream>  
\#include<string>  
\#include<fstream>  
using namespace std;

struct studentID \{  
studentID(): name(),address() \{\}  
studentID(string newname, string newaddress): name(newname), address(newaddress) \{\}  
string name;  
string address;  
\};

int main()  
\{  
map<int, studentID> studentID\_table;  
int key;  
string temp\_name, temp\_address;  
ifstream inFile("newfile.txt");  
while(!inFile.eof())  
\{  
inFile >> key >> temp\_name >> temp\_address;  
studentID\_table\[key\]= studentID(temp\_name,temp\_address);

inFile.close();  
map<int, studentID>::iterator map\_it = studentID\_table.begin();

for( map\_it = studentID\_table.begin(); map\_it != studentID\_table.end(); map\_it++) \{  
cout << "number:" <<endl;  
cout << map\_it->first << endl;  
cout << "the name is" << endl;  
cout << map\_it->second.name<<endl;  
cout << "the address is"<< endl;  
cout << map\_it->second.address<<endl;  
\}  
return 0;

查找key是否存在在map中，如果存在就输出，如果不存在什么也不做

\#include<map>  
\#include<iostream>  
\#include<string>  
\#include<fstream>  
using namespace std;  
  
  
struct studentID \{  
studentID(): name(),address() \{\}  
studentID(string newname, string newaddress): name(newname), address(newaddress) \{\}  
string name;  
string address;  
\};  
  
  
int main()  
\{  
map<int, studentID> studentID\_table;  
int key;  
string temp\_name, temp\_address;  
ifstream inFile("newfile.txt");  
while(!inFile.eof())  
\{  
inFile >> key >> temp\_name >> temp\_address;  
studentID\_table\[key\]= studentID(temp\_name,temp\_address);  
\}  
  
  
inFile.close();  
map <int, studentID>::iterator map\_it;  
if((map\_it=studentID\_table.find(66))!= studentID\_table.end()) \{  
cout << studentID\_table.find(66)->second.name << studentID\_table.find(66)->second.address << endl;  
\}  
return 0;  
\}