Joining many text files into one

[leszekj]

I have 153 text files that I named "1", "2", ..., "153". I wanted to join them into one file named "all.txt". I tried to do this through the code:

#include <cstdlib>
#include <iostream>
#include <cstring>
#include <fstream>
#include <sstream>

using namespace std;

int main(int argc, char *argv[])
{
    ofstream out("all.txt");
    for (int i=1; i<154; i++) {
        string s_line;
        char* s_file;
        // here the missing code to change integer i into the char s_file
        //  ??????????????
        ifstream in(s_file);
        while (getline(in, s_line)) {
            out << s_line << "\n";
        }
    }
    return 0
}

I put into the missing part of the code some functions changing integer into char (or string) in many different ways but nothing worked. Now I am going to try to use iterators but the solution seems so simple that I am asking for any help!

[chrisname]

Try int(s_file);. I'm not sure about C-strings but it works for normal char-int conversion.

Edit: I just realised you want to put i into the character string.

Here's how:
s_file = ("%d", i);
You need to use string formatting, like you would in printf();.
%d is decimal formatting, the integer is in base-10 (decimal) and therefore it's %d.



How big are the files? I found that when trying to merge large files, fstream:: couldn't handle them (they were half a GB each, mind) and ended up writing a batch file.

[Gregor]

dunno about c++ way, but since you already have cstdio...

//allocate space 
sfile = new char[16];//Up to 15 digit numbers
sfile[0]='\0'; //we're dealing with c-style strings now
sprinf(sfile, "%d", i);
//you've done it! 

[leszekj]

Thank you for your help. But chrisname, your instruction seems not to work. Gregor, your solution works but I am not sure whether the instruction s_file[0]='\0' is necessary. Here is the code that works ok:

#include <iostream>
#include <cstring>
#include <fstream>

using namespace std;

int main(int argc, char *argv[])
{
    ofstream out("all2.txt");
    char* s_file = new char(16);
    for (int i=1; i<154; i++) {
        string s_line;
        //s_file[0]='\0'; - is this really needed?
        sprintf(s_file, "%d", i);
        ifstream in(s_file);
        while (getline(in, s_line)) {
            out << s_line << "\n";
        }
    }
    return 0;
}

I must confess that I managed to solve the problem before but in a not very elegant way. I used Excel to produce 153 copies of the three lines of instructions:

  ifstream in1("1");
  while (getline(in1,s)) out << s << "\n";
  in1.close();
  ifstream in2("2");
  while (getline(in2,s)) out << s << "\n";
  in2.close();
  ........

...and it worked.
I hope that there is another - pure C++ - solution to this.

[Duthomhas]

Argh, why not just use the STL?

#include <fstream>
#include <sstream>
#include <string>
using namespace std;

...

for (unsigned n = 0; n < FOO; n++)
  {
  ostringstream filename;
  filename << n << ".txt";
  ifstream f( filename.str().c_str() );
  ...
  }

[leszekj]

Thanks, it works perfectly! Here is the whole program I checked:

#include <fstream>
#include <sstream>
#include <string>
using namespace std;
int main()
{
    ofstream out("outputfile.txt");
    string line;
    for (int i=1; i<5; i++) {
        stringstream filename;
        filename << i << ".txt";
        ifstream in( filename.str().c_str() );
        while (getline(in, line)) {
            out << line << "\n";
        }
    }
    return 0;
}

I changed here the "ostringstream filename;" into "stringstream filename;" - have no idea what the difference is. Another unclear point for me is the double usage of "str-like" functions in "filename.str().c_str()". But I think I will find the answer soon. Thanks again!

[Duthomhas]

An ostringstream is an output stringstream (which uses the << operator, just like cout).

A stringstream is not a string, so to get the string out of a stringstream, you must use the str() method.

The constructor for a file stream does not take a string -- it takes a const char*, which you get from a string with the c_str() method.

Glad to have helped. :-)