reorganized all the arduino/ docs into a lang/ subdirectory since

they're properly CC attributed now.

1 files changed, 57 insertions, 0 deletions

diff --git a/source/lang/static.rst b/source/lang/static.rst
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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