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Is there a function in C ++ that creates a .bin file, or is this code missing something?

I have some code that looks like this:

int main () {
  fstream file;
  file.open("test.bin", ios::out | ios::binary);
  if(!file.is_open())
  {
      return -1;
  }
  int n = 3;
  file.write(reinterpret_cast<char*>(&n), sizeof(n));
  file.close();
  return 0;
}

when i run it alone it exits at -1, so obviously it failed to open "test.bin". However, if I save a blank notepad as "test.bin" and run it, it works fine. I'm wondering how I can get my C ++ program to automatically generate an empty "test.bin" file if a file named "test.bin" doesn't exist yet.

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3 answers


Your code snippet is not correct as it is trying to write the file you opened for input. If you want to write a file, just use ios::out

instead ios::in

.

If you want to open the file for reading, but create it if it doesn't exist, you can use:

file.open("test.bin", ios::in | ios::binary);
if(!file.is_open()) {
    file.open("test.bin", ios::out | ios::binary);
    int n = 3;
    file.write(reinterpret_cast<char*>(&n), sizeof(n));
    file.close();
    file.open("test.bin", ios::in | ios::binary);
    if(!file.is_open()) {
        return -1;
    }
}


This will initialize the file with integer 3 as the default content if it doesn't already exist.

If it exists, it will leave the content alone. In any case, you will open the file in the first byte.

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Suppose you could just do this by opening and closing the file:



if (GetFileAttributes("test.bin") == INVALID_FILE_ATTRIBUTES)
{
    fstream file;
    file.open("test.bin", ios::out);
    file.close();
}
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One option is to open for read / write and search for the beginning of the file.

Then you can read, write, or do whatever you want.

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