c++ reading file using getline and FILE instead of ifstream

Question

I have a FILE* object from which I want to read line by line. The most common approach however is to pass a directory to ifstream and use getline(ifstream, line) in a while loop to read line by line.

However I do not have a directory. I have to work with FILE*. Is there a getline() that accepts a FILE* as parameter? or, in general is there another way in c++ to read lines with FILE*

C read file line by line does not work for me since i'm not on linux.

I was also thinking if an ifstream can accept a FILE instead of a directory but I am not sure about this. can anyone confirm?

There are various other portable solutions in the answers you linked to, what is wrong with those? — Alan Birtles, Jun 13 '19 at 07:43
You could try https://www.boost.org/doc/libs/1_70_0/libs/iostreams/doc/classes/file_descriptor.html#overview — Alan Birtles, Jun 13 '19 at 07:46
@camp0 I would appreciate an example since I am new to this. — bcsta, Jun 13 '19 at 07:57
It is not hard to build a getline clone from fgets. A bit of memory allocation and it is done... — Serge Ballesta, Jun 13 '19 at 07:57
There are `istream`/`istreambuf` implementations floating around that wrap `FILE*`. — Remy Lebeau, Jun 13 '19 at 08:12

Narase · Answer 1 · 2019-06-13T08:18:42.177

2

std::vector<std::string> getFileAsLines(FILE *file) {
  std::vector<std::string> out;
  int currentIn = fgetc(file);
  std::string currentLine;

  while(currentIn != EOF) {
    if (currentIn == '\n') {
      out.push_back(currentLine);
      currentLine = std::string();
    } else {
      currentLine += (char)currentIn;
    }

    currrentIn = fgetc(file);
  }
  out.Push_back(currentLine);
  return out;
}

Didnt test it, but the idea should go through

edited Jun 13 '19 at 08:18

answered Jun 13 '19 at 07:47

Narase

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2
12

In your while condition it should be `&&` or `and` not `AND` – john Jun 13 '19 at 07:53
@Narase so as a termination, while(line = getNextLine(File*file) != NULL) should work right? since 'out' is initially empty – bcsta Jun 13 '19 at 08:07
No, an empty string is not NULL since its not a pointer. Looks like youre coming from Java/C#. I edited the function so it returns the whole file as list of lines – Narase Jun 13 '19 at 08:23

c++ reading file using getline and FILE instead of ifstream

1 Answers1