122 lines
4.7 KiB
HTML
122 lines
4.7 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html>
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<head>
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<title>Arduino - Static </title>
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<div class="title"><a href="http://www.arduino.cc"/>Arduino</a></div>
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<p><a class='wikilink' href='http://arduino.cc/en/Main/Buy'>Buy</a>
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<a class="urllink" href="http://www.arduino.cc/blog/" rel="nofollow">Blog »</a> |
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<p><strong>Reference</strong> <a class='wikilink' href='index.html'>Language</a> (<a class='wikilink' href='Extended.html'>extended</a>) | <a class='wikilink' href='Libraries.html'>Libraries</a> | <a class='wikilink' href='Comparison.html'>Comparison</a>
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</p>
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<p class='vspace'></p><h2>Static</h2>
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<p>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.
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</p>
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<p class='vspace'></p><p>Variables declared as static will only be created and initialized the first time a function is called.
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</p>
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<p class='vspace'></p><h4>Example</h4>
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<pre>
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/* RandomWalk
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* Paul Badger 2007
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* RandomWalk wanders up and down randomly between two
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* endpoints. The maximum move in one loop is governed by
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* the parameter "stepsize".
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* A static variable is moved up and down a random amount.
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* This technique is also known as "pink noise" and "drunken walk".
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*/
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#define randomWalkLowRange -20
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#define randomWalkHighRange 20
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int stepsize;
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int thisTime;
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int total;
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void setup()
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{
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Serial.begin(9600);
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}
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void loop()
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{ // tetst randomWalk function
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stepsize = 5;
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thisTime = randomWalk(stepsize);
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Serial.println(thisTime);
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delay(10);
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}
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int randomWalk(int moveSize){
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static int place; // variable to store value in random walk - declared static so that it stores
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// values in between function calls, but no other functions can change its value
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place = place + (random(-moveSize, moveSize + 1));
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if (place < randomWalkLowRange){ // check lower and upper limits
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place = place + (randomWalkLowRange - place); // reflect number back in positive direction
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}
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else if(place > randomWalkHighRange){
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place = place - (place - randomWalkHighRange); // reflect number back in negative direction
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}
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return place;
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}
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</pre>
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<p class='vspace'></p><p><a class='wikilink' href='index.html'>Reference Home</a>
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<p class='vspace'></p><p><em>Corrections, suggestions, and new documentation should be posted to the <a class='urllink' href='http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?board=swbugs' rel='nofollow'>Forum</a>.</em>
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</p>
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<p class='vspace'></p><p>The text of the Arduino reference is licensed under a
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<a class='urllink' href='http://creativecommons.org/licenses/by-sa/3.0/' rel='nofollow'>Creative Commons Attribution-ShareAlike 3.0 License</a>. Code samples in the reference are released into the public domain.
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