For a nice treatment of file I/O, read the instructional material in http://www.cs.hmc.edu/~geoff/classes/hmc.cs070.200109/notes/io.html.
To illustrate, take a look at wordprint.cpp:
#include <iostream>
#include <fstream>
using namespace std;
main(int argc, char **argv)
{
ifstream in_fp;
ofstream out_fp;
string s;
if (argc != 3) {
cout << "Usage: wordprint inputfile outputfile\n";
exit(1);
}
in_fp.open(argv[1]);
if (in_fp.fail()) {
cout << "Couldn't open " << argv[1] << endl;
exit(1);
}
out_fp.open(argv[2]);
if (out_fp.fail()) {
cout << "Couldn't open " << argv[2] << endl;
exit(1);
}
while (!in_fp.fail()) {
in_fp >> s;
if (!in_fp.fail()) out_fp << s << endl;
}
}
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Note, it opens the file specfied by the first command line for reading, and it opens the file specified by the second command line for writing. It then reads in every word from the first file, and writes it on its own line in the second file. Note the use of the fail() method to test for successfull opening, and for testing for the end-of-file. Here it is working. Note how on my last call, I use a file in another directory:
UNIX> g++ -o wordprint wordprint.cpp UNIX> wordprint Usage: wordprint inputfile outputfile UNIX> cat input.txt This latest exponent of heresy is goaded into an attack. UNIX> wordprint input.txt output.txt UNIX> cat output.txt This latest exponent of heresy is goaded into an attack. UNIX> cat /home/plank/cs102/Examples/5A/5a-4.txt 25 a b c d e f g $ ~ UNIX> wordprint /home/plank/cs102/Examples/5A/5a-4.txt output.txt UNIX> cat output.txt 25 a b c d e f g $ ~ UNIX>