overwrite an fstream object

[John Smith]

I would like to write over a file if it exists (or create one if
it doesn't exist). The following codes do nothing if the file
already exists. How do I get it to overwrite an existing file?

Also, if the existing file is longer than what's going to be
written, how do I erase the excess portion of the existing file?

fsF.open ("test.txt", ios:ut|ios::trunc);
if (fsF.fail())
{
cout << "File test.txt cannot be opened.";
fsF.clear();
}

fsF << something

fsF.close();

 

[Mike Wahler]

I would like to write over a file if it exists (or create one if
it doesn't exist). The following codes do nothing if the file
already exists. How do I get it to overwrite an existing file?

std:fstream ofs("filename");

if(ofs)
std::cerr << "file created or truncated\n";
else
std::cerr << "failed to create or truncate file\n";

Also, if the existing file is longer than what's going to be
written, how do I erase the excess portion of the existing file?

See above.

-Mike

 

[John Smith]

std:fstream ofs("filename");

if(ofs)
std::cerr << "file created or truncated\n";
else
std::cerr << "failed to create or truncate file\n";

Thanks. Changing from fstream to ofstream did the trick, but why?

 

[Mike Wahler]

Thanks. Changing from fstream to ofstream did the trick, but why?

Read about the default parameters for the various fstream types.

-Mike