Question

this may be a simple problem, but i am not able to figure it out. I have structure like this.

struct emp 
{
  int empid;
  string fname;
}
emp e[10];

I have some data in e[10].

e[0].empid = 1 , e[0].fname = "tanenbaum"
e[1].empid = 2 , e[1].fname = "knuth"
.....

Now if i have given input command line like this:

emp , empid

Now i need to access the structure emp.empid. If i have 10 other structures, i need to access them, when the input gives like structure tag and structure member. Here i am not able to figure out how to attach string variables(emp, empid) to structure members(emp.empid). thanks in advance.
EDIT
Here is my program.

int main(int argc, char *argv[])
{
  char *tag_name = argv[1]; //emp (structure tag name)
  char *member_name = argv[2]; // empid (structure member name)
  int data = argv[3]; //value: 2
  /* I need some mechanism that will convert those tag_name.member_name
     to original structure memmber access

     tag_name(emp).member_name(empid) == value (2)
     Is there any way to map like this
*/
return ;
}

Answer 1

EDIT: Using pointer to member operator you can achieve what you wanted.
You need to create small database using std::map.

Below is the working program.

#include <iostream>
#include <string>
#include <map>
using namespace std;
struct emp 
{
  int empid;
  int salary;
};

int main(int argc, char *argv[])
{
    //member map stores member varialbe names and corresponding offsets.
    map<string, int emp::*> memberMap; //It can store offsets of only integer members.

    //tagMap stores tag names and object pointer
    map<string, emp *> tagMap;

    //Allocate for 10 records
    emp *e = new emp[10];
    //Store sample data in those records.
    for(int i = 0; i < 10; i++)
    {
        e[i].empid = (i+1) * 10;
        e[i].salary = (i+1) * 1000;
    }

    //Populate tag map with tag names and corresponding object pointers
    //As of now, we have only emp structure.
    //You can add more structures similar to below.
    tagMap.insert(pair<string, emp *>("emp", e));

    //Get the offsets of member variables of emp structure.
    int emp::*offset_empid = &emp::empid;
    int emp::*offset_salary = &emp::salary;

    //Populate member map with member names and corresponding offsets
    memberMap.insert(pair<string, int emp::*>("empid", offset_empid));
    memberMap.insert(pair<string, int emp::*>("salary", offset_salary));

    //Am passing tag name in argv[1], member name in argv[2] and record id in argv[3] from
    //command line
    string tagName = argv[1]; //tag name
    string memberName = argv[2]; //member name
    int recordId = atoi(argv[3]);//record id

    //Access member specified like below.
    cout<<"Employee details requested are : "<<endl;
    cout<<memberName<<"\t"<<(tagMap[tagName]+recordId)->*memberMap[memberName];

    //Free the allocated memory.
    delete []e;
}

Input:

emp salary 2

Output:

Employee details requested are :
salary 3000

I hope you can understand the program using comments i wrote.

Input: i am providing tagName, fieldName and recordId.

Output: i am getting the requested field value from requested record id.