Alternatives to ios::nocreate and ios::noreplace

In pre-standard C++, certain implementations of offered the flags ios::nocreate and ios::noreplace for controlling file creation. These flags were too platform-specific and never made it into the standard library, which supersedes the deprecated, pre-standard header. However, you can achieve the functionality of these obsolete flags rather easily. The following example imitates the ios::nocreate flag. First, it attempts to open a file for read. If the file doesn’t exist, no new file is created. If the file exists, the program closes it and reopens it in write mode:

fstream fs(“fname”, ios_base::in);// attempt open for read
if (!fs)
{
// file doesn’t exist; don’t create a new one
}
else //ok, file exists. close and reopen in write mode
{
fs.close();
fs.open(“fname”, ios_base::out); // reopen for write
}

You can just do the opposite for ios::noreplace:

fstream fs(“fname”, ios_base::in);// attempt open for read
if (!fs)
{
// file doesn’t exist; create a new one
fs.open(“fname”, ios_base::out);
}
else //ok, file exists; close and reopen in write mode
{
fs.close()
fs.open(“fname”, ios_base::out); // reopen for write
}

広告