Computer Science Canada :: View topic - generic code for writing structures, help me make it more generic

#include <iostream>
#include <fstream>
#include "exportimportstructdec.h"
using namespace std;

extern grades myGradesi, myGradeso, myGradesa;
extern grades *pMyGradeso, *pMyGradesa, *pMyGradesi;

//the purpose of this program is to send structures into a file, and then read them from the same file
//structure to be written:

void readfile(char readFileName[],grades structi,grades * pStructi)
{
//check the size of the file and allocate appropriate memory:
long begin,end;
ifstream filecheck (readFileName);
if (filecheck.is_open())
{
begin = filecheck.tellg();
filecheck.seekg (0, ios::end);
end = filecheck.tellg();
filecheck.close();
int fileSize=(end-begin)/(sizeof(structi));
pStructi= new grades [fileSize];
}
else cout << "\nUnable to open file for size check\n";
//read the file into memory:
int structArraySize=0;
ifstream filei;
filei.open (readFileName, ios::in|ios::binary);
if (filei.is_open())
{
while ((filei.peek()!=EOF))
{
filei.read(reinterpret_cast<char*>(&pStructi[structArraySize]), sizeof(grades));
structArraySize++;
}
//display memory on screen:
printmemory(structArraySize,pStructi);
}
else cout << "\nUnable to open file for input\n";
}

void wrtfile(char wrtFileName[],char wrtMessage[],grades structo,grades * pStructo)
{
ofstream fileo;
fileo.open (wrtFileName, ios::out|ios::binary);
cout << wrtMessage;
scanstruct(pStructo);
if (fileo.is_open())
{
fileo.write (reinterpret_cast<char*>(pStructo), sizeof(structo));
fileo.close();
}
else cout << "\nUnable to open file for output\n";
}

void appfile(char appFileName[],char appMessage[],grades structa,grades * pStructa)
{
ofstream filea;
filea.open (appFileName, ios::app|ios::binary);
cout << appMessage;
scanstruct(pStructa);
if (filea.is_open())
{
filea.write (reinterpret_cast<char*>(pStructa), sizeof(structa));
filea.close();
}
else cout << "\nUnable to open file for output\n";
}

void scanstruct(grades * pStructscan)
{
cin >> (*pStructscan).grade1 >> (*pStructscan).grade2 >> (*pStructscan).grade3 >> (*pStructscan).grade4;
}

void printmemory(int specificStructArraySize,grades * pStructi)
{
for(int i=0;i<specificStructArraySize;i++)
{
cout<<"\ngrade1\n"<< (pStructi[i]).grade1<<"\ngrade2\n"<< (pStructi[i]).grade2<<"\ngrade3\n"<< (pStructi[i]).grade3<<"\ngrade4\n"<< (pStructi[i]).grade4<<"\n";
}
}

Author:	Rigby5 [ Thu Oct 09, 2008 10:43 pm ]
Post subject:	RE:generic code for writing structures, help me make it more generic
Not too bad of a start. The difference between classes and structs is really insignificant, in how the default public vs private. So you don't really need to use classes. You can add member functions to a struct as well. But not many people do that, so I would switch to classes if you need member functions to manipulate the data in a group like a struct or class. So how do you make it more generic? Right now you have a fixed number of 4 integers in the struct. A more generic way would be to have an integer that tells you how many values is stored, and then have an array of that size that actually has the integers in it. That way the number can grow or shrink as necessary. Initially the counter value would be 0, and the array would be of size 0, or just a pointer of type integer. But every time you wanted to change the amount of data, you still would need make a new array, copy over any old data to the new array of a different size, and delete the old array. A better way is to not use arrays at all, but to make a linked list. Each node is a struct with only a single data value, and a pointer to the next struct in the list. If you don't want to learn about linked lists, then you could use an existing one, like from the Standard Template Library, (STL), which has things like VECTOR, etc.