File Append operation in c++

[mickey22]

Hi all,

I have to create a text file containing a set of results and I have used as
ofstream fout("results.txt,ios::out|ios::app);
where results.txt is the file I would like to put the data.

When I run the code for the first time it is displaying the results in the file properly.But when I execute my program again it append new results to the old results as I am using ios::app.If i dont use ios::app I am not getting the output when I execute for the first time.

How can I clear my initial results each time I run my program?Could anyone give me suggestions

Thanks.

[RRick]

It sounds like it should work. For example:

ofstream out;
out.open( "t.dat", ios::out);

Will open a file and truncate the file each time it is open.

out.open( "t.dat", ios::out|ios::app);

Will open a file and append info to the end of the file.

If this is what your code looks like, I would look at your code more closely for other issues. Are you closing the file? Are you checking for errors? Try a real simple test to see if it works or not.

[weaknessforcats]

When I run the code for the first time it is displaying the results in the file properly.But when I execute my program again it append new results to the old results as I am using ios::app.If i dont use ios::app I am not getting the output when I execute for the first time.

Don't use ios::app. Use ios::beg instead.

That way each time you opne then file is written from the beginning.

BTW, ios is the old form. You should be using ios_base::beg, etc. LIke this:

ofstream f("data.txt", ios_base::out | ios_base::beg);
 

[Girish Kanakagiri]

Hi all,

I have to create a text file containing a set of results and I have used as
ofstream fout("results.txt,ios::out|ios::app);
where results.txt is the file I would like to put the data.

When I run the code for the first time it is displaying the results in the file properly.But when I execute my program again it append new results to the old results as I am using ios::app.If i dont use ios::app I am not getting the output when I execute for the first time.

How can I clear my initial results each time I run my program?Could anyone give me suggestions

Thanks.

If you want to clear the initial results then
use ios::trunc
This clears your previous results. Make use of this only once at every execution. You can check this by setting a counter.

Regards,
Girish.

[mickey22]

The problem is that I have called ofstream("results.txt",ios::out); in a function say function1 and I have to call this function from function2 .

Each time I call this function1 from function2 the above statement fstream is being called and ios::out is creating new output file.

In case if I place ios::app I am not able to clear the contents when I run the program each time.

In what way can I put the conditions more clearly?Could anyone please suggest.

please let me know if my question is not clear.thanks

[weaknessforcats]

Did you not read Post #3 and Post #4 ??