editfile.cpp

/*

  g++ -Wall -O2 editfile.cpp -o editfile 

*/
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/sendfile.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <fstream>
#include <iostream>
#include <string>
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <array>


using namespace std;

int main(int argc, char **argv)
{
    ifstream in(argv[1]);
    ofstream out(argv[2]);
    string wordToReplace(argv[3]);
    string wordToReplaceWith(argv[4]);

    if (!in)
    {
        cerr << "Could not open " << argv[1] << "\n";
        return 1;
    }

    if (!out)
    {
        cerr << "Could not open " << argv[2] << "\n";
        return 1;
    }

    string line;
    size_t len = wordToReplace.length();
    while (getline(in, line))
    {
        while (true)
        {
            size_t pos = line.find(wordToReplace);
            if (pos != string::npos)
                line.replace(pos, len, wordToReplaceWith);
            else 
                break;
        }
        out << line << '\n';
    }
    std::string command;
    std::string inputFile(argv[1]);
    std::string outputFile(argv[2]);

    in.close();
    out.close();



    int read_fd;
    int write_fd;
    struct stat stat_buf;
    off_t offset = 0;

    /* Open the input file. */
    read_fd = open (argv[2], O_RDONLY);

    /* Stat the input file to obtain its size. */
     fstat (read_fd, &stat_buf);

    /* Open the output file for writing, with the same permissions as the
      source file. */
    write_fd = open (argv[1], O_WRONLY | O_CREAT, stat_buf.st_mode);

    /* Blast the bytes from one file to the other. */
    sendfile (write_fd, read_fd, &offset, stat_buf.st_size);

    close (read_fd);
    close (write_fd);

    return 0;
}