C++ file handling - c++

Question

I have two text files "source1" and "source2" that contain integers 3 4 1 2 56 and 2 45 34 23 45 respectively.
Displaying them on the screen.
Even though there is not any error given but what i am sure is that those array isn't getting the correct data from the files source1 and source2.
The ouput should be the integers in the file but it's not what i expected.
i guess there is some problem with my READ and WRITE.
#include<stdio.h>
#include<fstream>
#include<iostream>
using namespace std;
int main()
{
fstream file1;
fstream file2;
file1.open("source1.txt");
file2.open("source2.txt");
int source1[20];
int source2[20];
file1.read((char*)&source1,sizeof(source1));
cout<<source1<<"\n";
file2.read((char*)&source2,sizeof(source2));
cout<<source2<<"\n";
}

Answer 1

Here are some issues I noticed with your program.
Reading Arrays
Your code reads in 20 integers, whether there are 20 or not. If the file contains 4 binary integers, how do you handle the error?
Your file ends with a .txt extension, so I assume the data is in human readable (text) format. The read method does not translate "123" into the number 123. The read method will save a mirror of the data, as is.
Arrays and cout
The C++ programming language's cout does not have facilities for printing arrays of integers. You'll have to use a loop to print them. Also, you should use a separator between the integers, such as tab, newline, comma or space.
Binary & Text writing
If you want to write the internal representation of a number, use ostream::write. If you want to use formatted or textual representation use operator>>.
If the integer is more than a byte wide you will need to know if the platform outputs the highest byte first (Big Endian) or last (Little Endian). This makes a big difference when you read the values back.
Use Vectors not Arrays
Vectors are easier to pass and they take care of dynamic growth. Arrays are fixed capacity by definition and require 3 parameters when passing: The array, the capacity, and the quantity of items in the array. With std::vector, only the vector needs to be passed because all the other information can be obtained by calling vector methods, such as vector::size().

Answer 2

When opening files in C or C++ to write binary data, you have to open them in binary mode. Use:
file1.open("source1.txt", ios::in | ios::binary);
file2.open("source2.txt", ios::out | ios::binary);
Or similar flags.

Answer 3

Here is working code that describes what you are trying to achieve:
#include <string>
#include <vector>
#include <iostream>
#include <fstream>
#include <algorithm>
bool readIntsFromFile( const std::string& strFilename, std::vector<int>& v ) {
std::fstream inFile;
inFile.open( strFilename.c_str(), std::ios_base::in );
if ( !inFile.is_open() ) {
return false;
} else {
int val;
while ( !inFile.eof() ) {
inFile >> val;
v.push_back( val );
}
}
inFile.close();
return true;
}
void sortVectors( const std::vector<int>& v1, const std::vector<int>& v2, std::vector<int>& out ) {
unsigned index = 0;
for ( ; index < v1.size(); ++index ) {
out.push_back( v1[index] );
}
index = 0;
for ( ; index < v2.size(); ++index ) {
out.push_back( v2[index] );
}
std::sort( out.begin(), out.end() );
}
int main() {
const std::string strFile1( "source1.txt" );
const std::string strFile2( "source2.txt" );
const std::string strOutput( "output.txt" );
std::vector<int> a;
std::vector<int> b;
std::vector<int> res;
if ( !readIntsFromFile( strFile1, a ) ) {
return -1;
}
if ( !readIntsFromFile( strFile2, b ) ) {
return -1;
}
sortVectors( a, b, res );
unsigned index = 0;
for ( ; index < res.size(); ++index ) {
std::cout << res[index] << " ";
}
std::cout << std::endl;
std::fstream out;
out.open( strOutput.c_str(), std::ios_base::out );
if ( !out.is_open() ) {
return -1;
} else {
index = 0;
for ( ; index < res.size(); ++index ) {
out << res[index] << " ";
}
}
out.close();
return 0;
}
Just make sure that your source1 & source2 text files are in the same directory
as your generated executable.