how get string vector from class in file?

**tord** · 06-17-2005

Hi,
how can I store a class of string vectors as a bin or text file? I tried a .write/.read method which compiles fine, but I get a run time access violation error. Please see code below. I am using VC++ 6.0 and 7.0. Many thanks!

tord

Code:

vector<string>Feeder(1500); int Min1 = 0; string sMess1;
vector<string>Reader(1500);

void CfeedertestDlg::OnBnClickedButton1()
{
mimix Mupp(Feeder);//declare empty class with empty string vector
	Feeder[Min1] = sMess1;//int Min1 and string sMess1 defined by other buttons, set in vector.
 	Mupp.SetD1(Feeder); //set vector with string sMess1 at position Min1 in class Mupp.

	ofstream fout1("MuppMem", ios::binary);//prepare file
	fout1.write((char*) &Mupp, sizeof Mupp);//write class to file
	fout1.close();
	Reader = Mupp.GetD1();//run time error here if loaded from bin/text class store file!
	string sMess2 = Reader[Min1];//get string and display in message box:
	char A[255];
	ofstream fout("bupp.txt");
	fout << sMess2;
	fout.close();
	ifstream fin("bupp.txt");
	fin >> A;
	CString cMess = A;
	MessageBox(A);
Reader.erase(Reader.begin(), Reader.end());
Feeder.erase(Feeder.begin(), Feeder.end());

}

mimix::mimix(vector<string>initD1)
{itsD1 = initD1;
}

mimix::~mimix(void)
{
}

void CfeedertestDlg::OnBnClickedButton6()
{
	string sMess3;
	mimix Mepp(Feeder);
ifstream fin2("MeppMem",ios::binary);
fin2.read((char*) &Mepp, sizeof Mepp);
	fin2.close();
	Reader = Mepp.GetD1();//problem here, but only if retrieved from file, see above!
	char B[255];
	ofstream fout4("buppo.txt");
	fout4 << sMess3;
	fout4.close();
	ifstream fin4("buppo.txt");
	fin4 >> B;
	CString cMess2 = B;
	MessageBox(B);
	
}

//from class file:
#pragma once
#include <iostream>
#include <fstream>
#include <string>
#include <vector>

using namespace std;

class mimix
{
public:
	mimix(vector<string>initD1);
	~mimix(void);

	void SetD1(vector<string>D1) {itsD1 = D1;}
	vector<string> GetD1() const {return itsD1;}

private:

	vector<string>itsD1;
};

**hk_mp5kpdw** · 06-17-2005

For writing, you need to iterate over the container and write each individual string in the vector to the file seperately, probably seperating them by newlines (text mode might be better for the I/O in this case). For reading you need to repeatedly get a line of text and push it into the vector. You cannot use the read/write file stream methods to do I/O with a vector... it doesn't work. As a shortcut, you might be able to use the copy function defined in the algorithm header to do both the reading and writing.

Code:

#include <vector>
#include <fstream>
#include <string>
#include <algorithm>
#include <iterator>

using namespace std;

...

vector <string> strVectOut, strVectIn;
ofstream out;
ifstream in;

...

// Write strVectOut vector to the "out" file
out.open("file.txt");  // Open in text mode
copy(strVectOut.begin(), strVectOut.end(), ostream_iterator<string>(out,"\n"));
out.close();

// Read from "in" file into strVectIn
in.open("file.txt");   // Open in text mode
copy(istream_iterator<string>(in), istream_iterator<string>(), back_inserter(strVectIn));
in.close();

If the strings contain whitespace (space, tabs, newlines) you might need to do the reading/writing differently.

I am unsure what you are trying to accomplish by creating the mimix wrapper. It doesn't really seem to do much for you.

**pianorain** · 06-17-2005

You can save strings (including those with whitespace) to a binary file by first saving the length of the string and then writing the string. To load, read the length of the string, and then read that many bytes. Similarly, when storing a vector, you can save the length of the vector, and then save each entry. To load, read the length of the vector, and then read that many entries.

**Daved** · 06-17-2005

When using pianorain's method, make sure you are sending the data in the string to the write function, not the string itself. The data() function would be appropriate for this use, or the c_str() function (but you must remember that the c_str() function will add a null to the end so if you want that null written to your file you will have to write an extra byte). When reading in, you should read into a character buffer, make sure there is a terminating null and then assign that character buffer to your string instance. Simply writing and reading the string instances would not work as you have seen because they often hold dynamic memory.

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