In this task, the job is to create a file called “output.txt”, and place in it the contents of the file “input.txt”, via an intermediate variable. In other words, your program will demonstrate: (1) how to read from a file into a variable, and (2) how to write a variable’s contents into a file. Oneliners that skip the intermediate variable are of secondary interest — operating systems have copy commands for that.
#include <iostream> #include <fstream> #include <string> using namespace std; int main() { string line; ifstream input ( "input.txt" ); ofstream output ("output.txt"); if (output.is_open()) { if (input.is_open()){ while (getline (input,line)) { output << line << endl; } input.close(); // Not necessary - will be closed when variable goes out of scope. } else { cout << "input.txt cannot be opened!\n"; } output.close(); // Not necessary - will be closed when variable goes out of scope. } else { cout << "output.txt cannot be written to!\n"; } return 0; }
Simpler version:
#include <iostream> #include <fstream> #include <cstdlib> int main() { std::ifstream input("input.txt"); if (!input.is_open()) { std::cerr << "could not open input.txt for reading.\n"; return EXIT_FAILURE; } std::ofstream output("output.txt"); if (!output.is_open()) { std::cerr << "could not open output.txt for writing.\n"; return EXIT_FAILURE; } output << input.rdbuf(); if (!output) { std::cerr << "error copying the data.\n"; return EXIT_FAILURE; } return EXIT_SUCCESS; }
Using istream- and ostream- iterators:
# include <algorithm> # include <fstream> int main() { std::ifstream ifile("input.txt"); std::ofstream ofile("output.txt"); std::copy(std::istreambuf_iterator<char>(ifile), std::istreambuf_iterator<char>(), std::ostreambuf_iterator<char>(ofile)); }
Even simpler way:
#include <fstream> int main() { std::ifstream input("input.txt"); std::ofstream output("output.txt"); output << input.rdbuf(); }
Content is available under GNU Free Documentation License 1.2.
