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Errors writing a vector to a file

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Join Date: Mar 2005

Posts: 11

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johnson9000 johnson9000 is offline

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Errors writing a vector to a file

Mar 1st, 2005

Why does my file operation code write random data over the first two numbers I store in the file.
The code compiles and runs without error messages, but
I try to store the vector [0 0 0 0 0] and instead I get [20520 2414 0 0 0].

I am using linux if that makes a difference.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <vector.h>
#include <fstream.h>
 
void write_to_file(const char * filename, vector<short> v)
{
	//const char * filename = "/home/johnson/data/data.txt";
	ofstream outf(filename);
	for(long i=0;i<v.size();i++)
	{
		outf << v[i];
		outf << " ";
	}
	outf.close();
}
 
vector<short> read_from_file(const char * filename)
		// there is probably a better way to write this function
{		
	vector<short> v;
	//const char * filename = "/home/johnson/data/data.txt";
	ifstream inf(filename);
	for(long i=0;i<v.size();i++)
	{
		inf >> v[i];
	}
	inf.close();
// I think there should be a return but my compiler doesn't give me an error
 
}
 
 
void testVector(vector<short> a)
{
	cout << "begin testVector | ";
	long max = a.size();
	for(short i=0;i<max;i++)
	{
		cout << a[i] << " ";
	}
	cout << endl;
}
 
int main()
{
vector<short> newVector;
for(short i=0;i<5;i++) newVector.push_back(0);
testVector(newVector);
write_to_file("/home/johnson/data/data1.txt", newVector);
testVector( read_from_file("/home/johnson/data/data1.txt") );
return(0);
}
#include <vector.h>
#include <fstream.h>

void write_to_file(const char * filename, vector<short> v)
{
	//const char * filename = "/home/johnson/data/data.txt";
	ofstream outf(filename);
	for(long i=0;i<v.size();i++)
	{
		outf << v[i];
		outf << " ";
	}
	outf.close();
}

vector<short> read_from_file(const char * filename)
		// there is probably a better way to write this function
{		
	vector<short> v;
	//const char * filename = "/home/johnson/data/data.txt";
	ifstream inf(filename);
	for(long i=0;i<v.size();i++)
	{
		inf >> v[i];
	}
	inf.close();
// I think there should be a return but my compiler doesn't give me an error
	
}


void testVector(vector<short> a)
{
	cout << "begin testVector | ";
	long max = a.size();
	for(short i=0;i<max;i++)
	{
		cout << a[i] << " ";
	}
	cout << endl;
}

int main()
{
vector<short> newVector;
for(short i=0;i<5;i++) newVector.push_back(0);
testVector(newVector);
write_to_file("/home/johnson/data/data1.txt", newVector);
testVector( read_from_file("/home/johnson/data/data1.txt") );
return(0);
}

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Join Date: Sep 2004

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Narue

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Re: Errors writing a vector to a file

Mar 1st, 2005

>// I think there should be a return but my compiler doesn't give me an error
Just because your compiler doesn't complain doesn't mean that there's no error.

I'm here to prove you wrong.

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Join Date: Mar 2005

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johnson9000 johnson9000 is offline

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Re: Errors writing a vector to a file

Mar 1st, 2005

i agree, however this code does work if i just add two extra numbers a the begining of my vector and then ignore the bad data that is written over them. But when I add a return at the end of my read_from_file function I get a compiler error.

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Join Date: Sep 2004

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Narue

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Re: Errors writing a vector to a file

Mar 1st, 2005

•

Originally Posted by johnson9000

i agree, however this code does work if i just add two extra numbers a the begining of my vector and then ignore the bad data that is written over them. But when I add a return at the end of my read_from_file function I get a compiler error.

Oh, it's all okay then. :rolleyes:

I'm here to prove you wrong.

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Join Date: Mar 2005

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johnson9000 johnson9000 is offline

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Re: Errors writing a vector to a file

Mar 1st, 2005

I have no idea why my code works the way it does.

shouldn't this code read and write vectors?

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
void write_to_file(const char * filename, vector<short> v)
{
	ofstream outf(filename);
	outf << v.size();
	for(long i=0;i<v.size();i++)
	{
		outf << v[i];
		outf << " ";
	}
	outf.close();
}
 
vector<short> read_from_file(const char * filename)
{	
	short size;
	vector<short> v;
	ifstream inf(filename);
	inf >> size;
	for(long i=0;i<size;i++)
	{
		inf >> v[i];
	}
	inf.close();
	return(v);
}
void write_to_file(const char * filename, vector<short> v)
{
	ofstream outf(filename);
	outf << v.size();
	for(long i=0;i<v.size();i++)
	{
		outf << v[i];
		outf << " ";
	}
	outf.close();
}

vector<short> read_from_file(const char * filename)
{	
	short size;
	vector<short> v;
	ifstream inf(filename);
	inf >> size;
	for(long i=0;i<size;i++)
	{
		inf >> v[i];
	}
	inf.close();
	return(v);
}

I've been trying for hours to understand why it crashes. Any help would be greatly appreciated.

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Narue

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Re: Errors writing a vector to a file

Mar 1st, 2005

>shouldn't this code read and write vectors?
No, and this is why:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
vector<short> v;
...
inf >> v[i];
vector<short> v;
...
inf >> v[i];

Tell me, what is the size of v? Where do you specify enough information for the vector to know that v[i] should be valid? You don't. What you have is an empty vector, and the subscript operator is an unchecked operation, so it tries to access the ith element of an empty vector, which will always fail no matter what value i has. Compare:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
void write_to_file(const char * filename, vector<short> v)
{
  ofstream outf(filename);
  outf << v.size() <<' '; // Notice the space, it's important
  for(long i=0;i<v.size();i++)
  {
    outf << v[i];
    outf << " ";
  }
  outf.close();
}
 
vector<short> read_from_file(const char * filename)
{	
  short size;
  ifstream inf(filename);
  inf >> size;
  vector<short> v(size);
  for(long i=0;i<size;i++)
  {
    inf >> v[i];
  }
  inf.close();
  return(v);
}
void write_to_file(const char * filename, vector<short> v)
{
  ofstream outf(filename);
  outf << v.size() <<' '; // Notice the space, it's important
  for(long i=0;i<v.size();i++)
  {
    outf << v[i];
    outf << " ";
  }
  outf.close();
}

vector<short> read_from_file(const char * filename)
{	
  short size;
  ifstream inf(filename);
  inf >> size;
  vector<short> v(size);
  for(long i=0;i<size;i++)
  {
    inf >> v[i];
  }
  inf.close();
  return(v);
}