Example
When creating a file stream, you can specify an opening mode. An opening mode is basically a setting to control how the stream opens the file.
(All modes can be found in the std::ios namespace.)
An opening mode can be provided as second parameter to the constructor of a file stream or to its open() member function:
std::ofstream os("foo.txt", std::ios::out | std::ios::trunc);
std::ifstream is;
is.open("foo.txt", std::ios::in | std::ios::binary);
It is to be noted that you have to set ios::in or ios::out if you want to set other flags as they are not implicitly set by the iostream members although they have a correct default value.
If you don't specify an opening mode, then the following default modes are used:
ifstream-inofstream-outfstream-inandout
The file opening modes that you may specify by design are:
| Mode | Meaning | For | Description |
|---|---|---|---|
app | append | Output | Appends data at the end of the file. |
binary | binary | Input/Output | Input and output is done in binary. |
in | input | Input | Opens the file for reading. |
out | output | Output | Opens the file for writing. |
trunc | truncate | Input/Output | Removes contents of the file when opening. |
ate | at end | Input | Goes to the end of the file when opening. |
Note: Setting the binary mode lets the data be read/written exactly as-is; not setting it enables the translation of the newline '\n' character to/from a platform specific end of line sequence.
For example on Windows the end of line sequence is CRLF ("\r\n").
Write: "\n" => "\r\n"
Read: "\r\n" => "\n"
