Writing Data to Files

Sweet Flame

I am trying to write data to a file so that I can open it later. I am trying to save the values of variable to the file. After the file has been opened, I input: "hours << day << endl;" "hours" is the outfile and "day" is a variable that I am trying to write into it. If I remove the "<

JonEngle

Order of operation precedence: hours << day << endl; is equal to hours << (day << endl); You want: hours << day; hours << endl;

Achim Klein

The associativity of << is 'left to right'. So: hours << day << endl; is equal to (hours << day) << endl; Only the associativity of unary and assignment operators is 'right to left'. You can see it here. Regards Achim Klein

We can do no great things, only small things with great love. - Mother Theresa

Sweet Flame

I changed it so that it reads: hours<

Anonymous

What's the class of your hours object ? Is it an ofstream ?

Achim Klein

And of which type is your day entity ? Is it just an int ?

We can do no great things, only small things with great love. - Mother Theresa

Achim Klein

Can you compile this ?

// --------
// Main.cpp
// --------
/**
* @file
* @brief Re: main()
* @version 0.1
*/

// --------
// Includes
// --------
#include <iostream>
#include <fstream>

// ---------------
// Used namespaces
// ---------------
using namespace std;

// -------------------------------
// Definition of the MyClass class
// -------------------------------
/**
* Foo.
*/
class MyClass
{

public:

// ------------
// Construction
// ------------

/// standard-constructor
MyClass();


// -------------
// Serialization
// -------------

/// writes the object to the passed stream
ostream& write(ostream& Stream) const;

private:

// ----------
// Attributes
// ----------

/// the first member
int m\_first;

/// the second member
int m\_second;

/// the third member
int m\_third;

};

// -------
// MyClass
// -------
/**
* The standard-constructor.
*/
MyClass::MyClass()
{
m_first = 1;
m_second = 2;
m_third = 3;
}

// -----
// write
// -----
/**
* Writes the object to the passed stream.
*/
ostream& MyClass::write(ostream& Stream) const
{
return Stream << "first : " << m_first << endl
<< "second : " << m_second << endl
<< "third : " << m_third;
}

// ----------
// operator<<
// ----------
/**
* ostream << MyClass
*/
ostream& operator<<(ostream& Stream, const MyClass& Object)
{
return Object.write(Stream);
}

// ----
// main
// ----
/**
* The application starts here.
*
* @param argc number of arguments
* @param argv list of arguments
*
* @return 0 if finished successfully
*/
int main(int argc, char** argv)
{
// ofstream cout("cout.txt");

cout << MyClass() << endl;

return 0;

}

We can do no great things, only small things with great love. - Mother Theresa

Sweet Flame

yes, hours is an ofstream.

Sweet Flame

yes, my "day" is an int

Sweet Flame

yes, i can

Achim Klein

Maybe the compiler gets confused by your included header files. Try to use: <string> instead of <string.h> <fstream> instead of <fstream.h> <iostream> instead of <iostream.h> ... And avoid mixing them up.

We can do no great things, only small things with great love. - Mother Theresa

David Crow

Something else is at play here. This works fine for me:

#include <fstream.h>

void main( void )
{
ofstream hours("c:\\file.txt");
int day = 20;
hours << day << endl;
}

"Take only what you need and leave the land as you found it." - Native American Proverb

Achim Klein

Yes, this problem is really a bit strange... On my system the following code causes a C2679 error:

#include <string>
#include <fstream.h>

int main(int argc, char** argv)
{
ofstream hours("Hours.txt");

hours << "Hallo" << std::endl;

return 0;

}

We can do no great things, only small things with great love. - Mother Theresa

David Crow

Writing string is different than writing int (your original problem). The ofstream class does not support writing string data. You have to provide that yourself:

#include <fstream>
std::ofstream &operator<<( std::ofstream &os, const std::string &str )
{
os << str.c_str();
return os;
}

"Take only what you need and leave the land as you found it." - Native American Proverb