Re: Help with binary I/O
zr wrote:
On Nov 11, 10:05 am, joseph.redime...@baesystems.com wrote:
Hi there,
I'm trying to save a vector data structure to a binary file, then read
it back and see if all the contents are intact. So I'm trying to
following code below :
#include "stdafx.h"
#include <stdio.h>
#include <vector>
#include <iostream>
#include <fstream>
using namespace std;
void main() {
main() must return int in C++.
//
// Create a test vector of integers and populate with test data
//
vector<int> int_ls;
int_ls.push_back(100);
int_ls.push_back(200);
int_ls.push_back(300);
int_ls.push_back(400);
int_ls.push_back(500);
//
// Dump the contents of the integer vector to a binary file
//
fstream binfile("fstream.out", ios::out|ios::binary);
binfile.seekp(0, ios::end);
binfile.write((char*)&int_ls,sizeof(int_ls));
binfile.close();
//
// Re-open the binary file and this time read the values and
store again in vector structure
//
vector<int> int_ls2;
fstream binfile2("fstream.out", ios::out|ios::in|ios::binary);
binfile2.seekg(0, ios::beg);
while (!binfile2.eof()) {
binfile2.read((char*)&int_ls2, sizeof(int_ls2));
}
binfile2.close();
//
// Now let's display what we just read in
//
int DATA_SIZE = int_ls2.size();
for (i=0; i<DATA_SIZE; i++) {
printf("\n int_ls2[%d] --> %d", i, int_ls2[i]);
};
}
** The above code manages to save to a file and even retrieve all the
values, but somehow I get an assert before it terminates.
** More info: I'm compiling it using Visual C++ 2008 as a Console
Application.
Thanks in Advance,
Joseph
A couple of errors i spotted:
1) binfile.write((char*)&int_ls,sizeof(int_ls));
sizeof(int_ls) returns the size of the container object. What you
probably meant was the size of the objects stored by the container
objects. A quick solution (perhaps not the most elegant) is:
binfile.write((char*)&int_ls.front(), int_ls.size()*sizeof int_ls[0]);
You shouldn't use int_ls.front() for one function arguemnt and int_ls[0] for
the other. They are both the same thing.
2) The while loop: similar problem as above. Try:
int buffer;
binfile2.read((char*)&buffer, sizeof(buffer));
while (!binfile2.eof()) {
int_ls2.push_back(buffer);
binfile2.read((char*)&buffer, sizeof(buffer));
}
This is more complicated than necessary. Also, it will result in an endless
loop filling up all available memory if any error happens to the stream
during reading. I'd rather suggest:
while (binfile2.read((char*)&buffer, sizeof(buffer)))
{
int_ls2.push_back(buffer);
}
Then after the loop, check if eof was reached or some error happened.