LEGO MINDSTORMS Robots Manual page 179

The rotation sensor code does not work in the March 30, 1999 build of legOS 0.1.7.
Using the Buttons (direct-button.h)
legOS provides one function and some other handy definitions to describe the state of the front panel buttons:
int button_state(void)
This function returns a value that indicates the state of the RCX's four buttons. Use the following macros to interpret the returned value.
PRESSED(state, button)
RELEASED(state, button)
These macros return a boolean value indicating if the specified button was pressed or not. To use these macros, pass the result of button_state() as the state parameter and the name
of a button for button. Buttons names are BUTTON_ONOFF, BUTTON_RUN, BUTTON_VIEW, and BUTTON_PROGRAM.
For example, the following code tests the state of the View button:
if (PRESSED(button_state(), BUTTON_VIEW)) {
// View button is pressed.
}
To test the state of more than one button, it makes sense to store the result of button_state(), like this:
int state;
state = button_state();
if (PRESSED (state, BUTTON_VIEW)) {
// View button is pressed.
}
if (PRESSED(state, BUTTON_PROGRAM) ) {
// Program button is pressed.
}
The Infrared Port (direct-ir.h)
To send data out the IR port, just use the dir_write() function:
size_t dir_write(void∗ const buf, size_t len)
This function writes len bytes of data from the supplied buffer out the IR port. It returns the number of bytes written or -1 if there is an error.
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