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.. highlight:: cpp
.. _lang-static:
``static``
==========
The ``static`` keyword can be used to create variables that are
visible to only one function. However, unlike local variables that get
created and destroyed every time a function is called, ``static``
variables persist beyond the function call, preserving their data
between function calls.
Variables declared as ``static`` will only be created and initialized
the first time a function is called.
.. note:: This is only one use of the ``static`` keyword in C++. It
has some other important uses that are not documented here; consult
a reliable C++ reference for details.
Example
-------
One use case for ``static`` variables is implementing counters that
last longer than the functions which need them, but shouldn't be
shared to other functions. Here's an example::
void setup() {
SerialUSB.begin();
}
void loop() {
int reading;
if (timeToReadSensors()) {
reading = readSensors();
}
// do something with reading
}
int readSensors() {
static int numSensorReadings = 0;
numSensorReadings++;
if (numSensorReadings % 100 == 0) {
SerialUSB.print("just got to another 100 sensor readings");
}
return analogRead(...);
}
In this example, the static variable ``numSensorReadings`` is
initialized to zero the first time ``readSensors()`` is called, and
then incremented, so it starts out at one. Subsequent calls to
``readSensors()`` won't reset ``numSensorReadings`` to zero, because
it was declared ``static``. Thus, ``numSensorReadings`` is a count of
the number of times that ``readSensors()`` has been called.
.. include:: cc-attribution.txt
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