Text file modifying

Hello there,

I have a problem of modifying a text file with C++.


Here is a text file "show.txt" that I want to modify.
Each line has one record and Each record is separated by '\n'.
And I want to correct 'c' of the movie title on the third line. ('c'ack to the Future)
-----------------------------------------------------------------
S001|terminator2|2009-10-29|02:10|X|0\n
S002|beautiful life|2009-10-30|02:11|P|1\n
S003|cack to the Future|2009-10-31|02:12|R|2\n
S004|Shindler List|2009-11-01|02:13|X|3\n
S005|the Matrix|2009-11-02|02:14|P|4\n
S006|Titanic|2009-11-03|02:15|R|5\n

Code:

---

int main(int argc, _TCHAR* argv[])
{
        fstream file;
        char str[100];
        streamoff size;

        file.open("show.txt", ios::in);
        file.getline(str, 50, '\n');
        file.getline(str, 50, '\n');
        size=file.tellp(); // I have the position of "cack to the Future" record.
        file.close();
       
        size+=5;// to point out the first letter of the movie title, 'c'
       
        file.open("show.txt", ios::out);
        file.seekp(size, ios::beg);
        file.write("b",1); //try to overwrite from "c" to "b"
        file.close();

                return 0;
}

---

I got the result bellow. (I just wanted to switch a character but everything has gone but 'b', it seems like that I have tried to modify.)
-----------------------------------------------------------------

b


Can anyone give me an advice?
Thank you.

C++ doesn't offer that kind of control. Usually you are forced to rewrite the entire file after changing it in RAM. Here's a minimal example of the way:

Code:

---

#include <string>
#include <fstream>
#include <cstdio>

int main()
{
  // declarations here

  while(std::getline(infile, str)) {
      std::string::size_type pos = str.find("cack to the future");
      if(pos != std::string::npos) {
        str[pos] = 'b';
        outfile << str << '\n';
      }
      else {
        outfile << str << '\n';
      }
  }
  infile.close();
  outfile.close();
  std::remove("show.txt");
  std::rename("show.temp", "show.txt");

  return 0;
}

---

Lots of fancier ways I suppose though. And you'll want to make sure that all file changes like rename and remove were successful.

Thank you for your help.
It's very useful lesson for me.!