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
- in
ofstream
- out
fstream
- in
and out
File opening modes:
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"