static

Description

The static keyword is 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.

Example Code

/* RandomWalk Paul Badger 2007 RandomWalk wanders up and down randomly between two endpoints. The maximum move in one loop is governed by the parameter "stepsize". A static variable is moved up and down a random amount. This technique is also known as "pink noise" and "drunken walk". */ #define randomWalkLowRange -20 #define randomWalkHighRange 20 int stepsize; int thisTime; void setup() { Serial.begin(9600); } void loop() { // test randomWalk function stepsize = 5; thisTime = randomWalk(stepsize); Serial.println(thisTime); delay(10); } int randomWalk(int moveSize) { static int place; // variable to store value in random walk - declared static so that it stores // values in between function calls, but no other functions can change its value place = place + (random(-moveSize, moveSize + 1)); if (place < randomWalkLowRange) { // check lower and upper limits place = randomWalkLowRange + (randomWalkLowRange - place); // reflect number back in positive direction } else if (place > randomWalkHighRange) { place = randomWalkHighRange - (place - randomWalkHighRange); // reflect number back in negative direction } return place; }

See Also

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