Question

I’ve got this code that uses an fstream to read and write to a file. The fstream object is held as a member of an object, and is initialized in the constructor like so:

idmap.open(path, std::fstream::in | std::fstream::out | std::fstream::app);

The file gets properly created if it doesn’t already exists. Then it gets written to like so:

idmap.seekp(0, std::fstream::end);
idmap << str.size() << ':' << str << '\n';
idmap.flush();
idmap.sync();

It’s supposed to be read like this but I don’t know if it works because the file has always been empty:

idmap.seekg(0);
while (!idmap.eof()) {
    idmap.getline(line, 1024);

    idtype id = getIDMapEntry(std::string(line));
    if (identifier.compare(nfile.getIdentifier()) == 0) {
        return nfile;
    }
}

Then it’s closed when the program exits:

idmap.close();

It’s probably something else in the program but I figure I’ll ask here in case I did something stupid, and dig through everything else in parallel.

Answer 1

Works for me.

This program, except for the .eof() bug, works precisely as expected:

#include <fstream>
#include <iostream>

int main() {
  std::fstream idmap;
  const char path[] = "/tmp/foo.txt";
  idmap.open(path, std::fstream::in | std::fstream::out | std::fstream::app);

  std::string str("She's no fun, she fell right over.");
  idmap.seekp(0, std::fstream::end);
  idmap << str.size() << ':' << str << '\n';
  idmap.flush();
  idmap.sync();

  idmap.seekg(0);
#if 1
  // As the user presented, with .eof() bug
  char line[1024];
  while (!idmap.eof())
  {
    idmap.getline(line, 1024);

    std::cout << line << "\n";
  }
#else
  // With fix for presumably unrelated .eof() bug
  std::string line;
  while(std::getline(idmap, line)) {
    std::cout << line << "\n";
  }
#endif

}