Cocos2d-x on the problem of random number acquisition, cocos2d-x Random Number

Cocos2d-x on the problem of random number acquisition, cocos2d-x Random Number

We used to get a random number when playing a game.

1 rand()%(end-start+1)+start;  

The end and start parameters are used to set the random number range. To obtain a random number that is close to the real number, you need to set a seed. The common method is to use the current time as the seed, A way to get time is provided in the cocos2d-x, And the get time is more accurate

1 cc_timeval psv;2     CCTime::gettimeofdayCocos2d(&psv, NULL);3     unsigned long int seed = psv.tv_sec*1000 + psv.tv_usec/1000;

The obtained time can be accurate to milliseconds.

The requirement of the project is to obtain a set of random numbers, which requires a loop to obtain a large number of random numbers. In the beginning, we did this:

 1 //CardDispatcher.cpp 2  3 int CCardDispatcher::getRandomNumber(){ 4         cc_timeval psv; 5     CCTime::gettimeofdayCocos2d(&psv, NULL); 6     unsigned long int seed = psv.tv_sec*1000 + psv.tv_usec/1000; 7     srand(seed); 8  9     int randNumber = random(0, 10);10     return randNumber;11 }12 13 int CCardDispatcher::random(int start, int end){14     15     return CCRANDOM_0_1()*end+start;16 17 }18 19 //MainGameLayer.cpp20 21 bool MainGameLayer::init(){22     CCLayer::init();23     this->schedule(schedule_selector(MainGameLayer::getCardNumber), 1.0);24     return true;25 }26 27 void MainGameLayer::getCardNumber(float dt){28     int randomNumber = CCardDispatcher::shareDispatcher()->getRandomNumber();29     CCLOG("%d", randomNumber);30 }

When debugging, we found that the random number obtained was quite regular ......

At that time, I felt very strange. I checked it online for a long time and did not find any problems (maybe I did not take a closer look at the tutorial, haha ). Later, I suddenly felt that I should put the set seed out of the loop, and then the source code was changed as follows:

 1 //CardDispatcher.cpp 2  3 int CCardDispatcher::getRandomNumber(){ 4     int randNumber = random(0, 10); 5     return randNumber; 6 } 7  8 int CCardDispatcher::random(int start, int end){ 9     10     return CCRANDOM_0_1()*end+start;11 12 }13 14 15 //MainGameLayer.cpp16 17 bool MainGameLayer::init(){18     CCLayer::init();19 20     cc_timeval psv;21     CCTime::gettimeofdayCocos2d(&psv, NULL);22     unsigned long int seed = psv.tv_sec*1000 + psv.tv_usec/1000;23     srand(seed);24     this->schedule(schedule_selector(MainGameLayer::getCardNumber), 1.0);25     return true;26 }27 28 void MainGameLayer::getCardNumber(float dt){29     int randomNumber = CCardDispatcher::shareDispatcher()->getRandomNumber();30     CCLOG("%d", randomNumber);31 }

Debugging is successful.

So, set the position of the seed to be placed outside the loop .....