The C language does not have any I/O capability! You can access files and devices via two groups of functions, these can be split as shown below.
Low level functions reference files by a file descriptor, this descriptor is created with the open function and can be referenced by functions like:
close
read
write
mmap - Memory map (Not supported on Linux).
ioctl I/O control.
Three 'file descripters' are opened automatically when your program runs. These are:
File Default Desc Name device ---- ---- ------ 0 stdin Keyboard 1 stdout Screen 2 stderr ScreenIf you want to use these 'file descriptors', you do not have to issue an 'open'.
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