fstream not creating new file

Question

I am trying to learn dynamic file access. My code is as follows:

int main()
{
    dtbrec xrec; // class object
    fstream flh;

    // Doesn't create a new file unless ios::trunc is also given.
    flh.open("database.txt", ios::in | ios::out | ios::binary);

    flh.seekp(0,ios::end);
    xrec.getdata();
    flh.write((char*)&xrec, sizeof(dtbrec));

    flh.close();
}

I thought that fstream by default creates a new file 'database.txt' if it doesn't exist. Any ideas as to what could be wrong?

Welcome to Stack Overflow! This question has been asked before: http://stackoverflow.com/questions/8835888/stdfstream-doesnt-create-file?rq=1 — Thom Wiggers, Jun 23 '13 at 11:43
@ThomWiggers wow, thank you but if ios::in is not specified how is the data stored in the file? — Stephen Jacob, Jun 23 '13 at 12:07
@AlexandruBarbarosie thankyou, i have an idea on how to use ifstream and outstream, but wanted to use fstream — Stephen Jacob, Jun 23 '13 at 12:08

score 20 · Accepted Answer · edited May 23 '17 at 12:34

20

Some pointers about fstream:

a. If you are using a back slash to specify the directory such as when using fstream f;

f.open( "folder\file", ios::out);

it won't work, a back slash has to be preceded by a backslash, so the correct way would be:

f.open( "folder\\file", ios::out);

b. If you want to create a new file, this won't work:

f.open("file.txt", ios::in | ios::out | ios::binary);

the correct way would be to first create the file, using either ios::out or ios::trunc

f.open("file.txt". ios::out) or f.open("file.txt", ios::trunc);

and then

f.open("file.txt", ios::in | ios::out | ios::binary);

c. Finally, it could be in this order as specified in this answer, fstream not creating file

Basically ios::in requires to already have an existing file.

edited May 23 '17 at 12:34

Community

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answered Aug 10 '13 at 10:05

Stephen Jacob

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Your examples show forward slashes, not backslashes. You do not need to escape forward slashes. – Buge Jul 31 '14 at 17:52
Thanks Buge I have edited it, I used backlash when I was learning about fstream. While I am aware and predominantly using forward slash now, I will not like to edit the content (using backslashes) as I personally believe that initially while learning fstream, this post may be useful especially to a newbie, however your comment can prove useful to them as well – Stephen Jacob Aug 01 '14 at 03:24

score 3 · Answer 2 · answered Jun 23 '13 at 12:38

Try using ofstream, it automatically creates a file, if it does not already exist. Or, if you want to do both input, and output on the stream, try using fstream, but you need not specify ios::in|ios::out|ios::binary, because fstream automatically sets it up for you.

score 0 · Answer 3 · answered Sep 28 '22 at 17:14

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In addition to what Stephen Jacob said, I found that I needed to do

f.open("file.txt", fstream::trunc | fstream::out);

on windows in order to actually generate the file. Just doing trunc didn't work.

answered Sep 28 '22 at 17:14

Hunter Keene

1

fstream not creating new file

3 Answers3