CODEWITHSUNDEEP
c++file-ioifstreamofstream
Alex Moumoulidis
Alex Moumoulidis

Reputation: 25

Text file I/O with fstream and ifstream

#include <iostream> 
#include <fstream> 
#include <cstdlib>

using namespace std;

int main(int argc, char *argv[]) 
{ 
    ifstream is; 
    is.open(argv[1]);
    ofstream outfile;
    outfile.open(argv[2]);
    char ch; 
    while (1) 
    { 
         ch = is.get();   // this is where test.txt is supposed
         outfile.put(ch); // to be copied to test2.txt
         if (is.eof()) 
             break; 
         cout << ch;  //this shows
    }

    is.close();
    outfile.close();

    ifstream outfile2;
    outfile2.open(argv[2]); 
    char ch2; 
    while (1)
    { 
       ch2 = outfile2.get(); 
       if (outfile2.eof()) 
         break; 
       cout << ch2;  //this doesnt
    }        
        outfile2.close();

        system("PAUSE"); 
        return 0; 
    }

I run it through cmd giving it 2 arguments test.txt test2.txt and it outputs what i have written in test.txt in cmd but test2.txt remains empty for some reason?

Upvotes: 0

Views: 861

Answers (2)

Saksham
Saksham

Reputation: 9390

for me its not coming blank but with some extra appended characters. this is because you are writing the character which you got from the old file to the new one before checking eof().

the code for writing from one file to another should be changed as

while (1) 
    { 
         ch = is.get();
         if (is.eof()) 
             break; 
         outfile.put(ch);
         cout << ch;  //this shows
    }

Upvotes: 0

Ulrich Eckhardt
Ulrich Eckhardt

Reputation: 17444

Please check the streamstate not just for eof() but also for failure. Also, after reading the last character, it wouldn't be uncommon if the streamstate was EOF even though the character was successfully read. Therefore, always try to read an element and if it succeeded, and only then, use the element:

ifstream in(argv[1]);
ofstream out(argv[2]);
char c;
while(in.get(c))
    out.put(c);

To make this really efficient, use this though:

out << in.rdbuf();

In any case, check the streamstate for success:

if(!in.eof())
    throw std::runtime_error("failed to read input file");
if(!out.flush())
    throw std::runtime_error("failed to write output file");

Upvotes: 1

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