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constructor and destructor

Posted on 2004-04-20
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Last Modified: 2010-04-01
I am told to write a constructor which accepts data from a file and writes it to a node and a destructor which reads data from the node to a file. I am not knowing what to pass as parameter for the destructors. Could you please give me a sample code. For example reading dates from file to date objects and a destructor reading the date objects and writing them to files.
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Question by:rmvprasad
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3 Comments
 
LVL 9

Expert Comment

by:Cayce
ID: 10870972
Something like this:

class MyClass {
private:
  Node MyNode;
  string FileName;
public:
  MyClass(string FileName) {
    this->FileName = FileName;
    // open file (filename) and write info to node
  }
  void ~MyClass() {
    // write node info to file (filename)
  }
};

Destructors never accept parameters, however all the object data is still valid at the time the destructor is called (unless it;s dynamically allocated and previously released).

This looks like homework, remember EE policies.
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LVL 2

Expert Comment

by:guntherothk
ID: 10871203
The purpose of a destructor is to clean up the resources allocated to a class instance before the instance is destroyed. The destructor doesn't need parameters because everything it needs to know is in the class instance. The most usual thing that happens in a destructor is to free memory or file handles owned by the instance.
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LVL 5

Accepted Solution

by:
allmer earned 40 total points
ID: 10871845
I assume that 'node' would be a node in, say a linked list.
#include <list>
using namespace std;
class MyClass {
typedef list<int> nodeList;
nodeList nodes;
nodeList::iterator listPos;
CString filePath
public:
  MyClass(CString _filePath) {
    filePath = _filePath;
    double value = 0;
    File *in = fopen(filePath,"r");
    while(!feof(in)) {
       fscanf("%f\n",value);
       nodes.push_back(value);
    }
    fclose(in)
  }
  void ~MyClass() {
    double value = 0;
    File *out = fopen(filePath,"w");
    for(listPos = nodes.begin(); listPos != nodes.end(); listPos++) {
        value = listPos;
        fprintf("%f\n",value);
    }
    fclose(out);
  }
};
I didn't do error checking so that is up to you
but I think it will lead you to what you are supposed to do.
Hope it helps,
Jens
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