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How to read one text file and store that in one variable in C++?

Piraisudan (3)
I am trying to read one text file and store all data from that text file into one string variable but how can I do that?
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        string ch;
	ifstream file("E:\\textfile1.txt");
	
	if (!file)
	{
		cout << "Error in opening file!!!" << endl;
		return -1; 
	}

	while (!file.eof())
	{
		file >> noskipws >> ch;	
		cout << ch;	
	}

	file.close();



How can I store all data in one variable? anyone give solution. Thanks in advance.
Last edited on
mbozzi (3932)
How can I store all data in one variable? anyone give solution. Thanks in advance. 


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# include <fstream>
# include <sstream>

int main() {
  std::ifstream file{"E:\\textfile1.txt"};
  
  std::string const file_contents = static_cast<std::ostringstream&>
      (std::ostringstream{} << file.rdbuf()).str();
}


Edit: the code I found the above in credits someone else:
/* Thanks, http://cpp.indi.frih.net */
Last edited on
Piraisudan (3)
How to read the entire file by iterating every character in the file?
lastchance (6980)
You could try one of these. The last one takes a bit of lateral thinking.

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#include <iostream>
#include <fstream>
#include <string>
#include <algorithm>
#include <iterator>
using namespace std;

int main()
{
   string allFile;

   ifstream file( "temp.cpp" );
   copy( istream_iterator<char>{ file >> noskipws }, {}, back_inserter( allFile ) );
   file.close();

   cout << "File contents:\n" << allFile;
}



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#include <iostream>
#include <fstream>
#include <string>
#include <algorithm>
#include <iterator>
using namespace std;

int main()
{
   char c;
   string allFile;

   ifstream file( "in.txt" );
   file >> noskipws;
   while ( file >> c ) allFile += c;
   file.close();

   cout << "File contents:\n" << allFile;
}



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#include <iostream>
#include <fstream>
#include <string>
#include <numeric>
#include <iterator>
using namespace std;

int main()
{
   ifstream file( "in.txt" );
   string allFile = accumulate( istream_iterator<char>{ file >> noskipws }, {}, string{} );
   file.close();

   cout << "File contents:\n" << allFile;
}
Thomas1965 (4571)
Another option:
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string read_file(const char *filename)
{
  stringstream buffer;

  buffer << ifstream(filename).rdbuf();

  return buffer.str();
}
JLBorges (13770)
Directly accessing the stream buffer and performing unformatted input is the most straightforward way to read the entire contents of a text stream into a string. It also happens to be the most efficient way of doing so.

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std::string contents_of( std::string path_to_file )
{
    std::ifstream file(path_to_file) ;
    return { std::istreambuf_iterator<char>(file), std::istreambuf_iterator<char>{} } ;
}
lastchance (6980)
Summary of methods above in a common form. My apologies if it doesn't reflect your intended style of coding.

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#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <algorithm>
#include <numeric>
#include <iterator>
using namespace std;


//======================================================================


string readFile1( string filename )                                            // @JLBorges : direct from stream buffer
{
   ifstream file( filename );
   return { istreambuf_iterator<char>(file), {} };
}


//======================================================================


string readFile2( string filename )                                            // @mbozzi / @Thomas1965 : via stringstream buffer
{
   stringstream buffer;
   buffer << ifstream( filename ).rdbuf();
   return buffer.str();
}


//======================================================================


string readFile3( string filename )                                            // @lastchance: copy / stream_iterator / back_inserter
{
   ifstream file( filename );
   string s;

   copy( istream_iterator<char>{ file >> noskipws }, {}, back_inserter( s ) );

   return s;
}


//======================================================================


string readFile4( string filename )                                            // @lastchance: just add chars
{
   char c;
   ifstream file( filename );

   string s;
   file >> noskipws;           // needed to prevent loss of spaces and linefeeds
   while ( file >> c ) s += c;

   return s;
}


//======================================================================


string readFile5( string filename )                                            // @lastchance: add chars with accumulate
{
   ifstream file( filename );
   return accumulate( istream_iterator<char>{ file >> noskipws }, {}, string{} );     
}


//======================================================================


void write( string s )
{
   cout << "File contents:\n" << s << "\n\n";
}


//======================================================================


int main()
{
   string filename = "in.txt";
   string s;

   s = readFile1( filename );   write( s );
   s = readFile2( filename );   write( s );
   s = readFile3( filename );   write( s );
   s = readFile4( filename );   write( s );
   s = readFile5( filename );   write( s );
}

Last edited on
closed account (E0p9LyTq)
How to read an entire file into memory in C++
http://cpp.indi.frih.net/blog/2014/09/how-to-read-an-entire-file-into-memory-in-cpp/
mbozzi (3932)
That's the one - thanks
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