Cocos2d-x on the problem of obtaining random numbers

Before you do a game, you need to get a random number.

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

The parameter end and start are set to get the range of random numbers, and to get close to the real random number you need to set a seed, the more common method is to use the current time as a seed, in the cocos2d-x to provide a way to get time, and get more accurate time

1 cc_timeval psv;2     cctime::gettimeofdaycocos2d (&PSV, NULL); 3     unsigned long int seed = psv.tv_sec*1000 + psv.tv_usec/1000;

The resulting time can be accurate to the millisecond level.

The requirement of a project is to get a set of random numbers, which is to use a loop to get a large number of random numbers, and at the beginning it does 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)     return randnumber;11}12 int ccarddispatcher::random (int start, int end) {     return ccrandom_ 0_1 () *end+start;16}18//maingamelayer.cpp20 bool Maingamelayer::init () {     cclayer::init ();     This->schedule (Schedule_selector (Maingamelayer::getcardnumber), 1.0),     return true;25}26-void Maingamelayer::getcardnumber (float dt) {     randomnumber = Ccarddispatcher::sharedispatcher () GetRandomNumber ();     Cclog ("%d", randomnumber); 30}

When debugging, we find that the random number is very regular ...

It was a strange feeling that I had been searching the internet for a long time, and I didn't find any problems (maybe I didn't watch the tutorial carefully, haha). Then suddenly feel, should not put the seed set to the outside of the loop, and then the source code changes as follows:

1//carddispatcher.cpp 2  3 int ccarddispatcher::getrandomnumber () {4     int randnumber = random (0, ten); 5     return randnumber; 6} 7  8 int ccarddispatcher::random (int start, int end) {9     return ccrandom_0_1 () *end+start;11 12}13 14 15 MAINGAMELAYER.CPP16-bool Maingamelayer::init () {     cclayer::init ();     cc_timeval psv;21     cctime:: Gettimeofdaycocos2d (&PSV, NULL);     unsigned long int seed = psv.tv_sec*1000 + psv.tv_usec/1000;23     srand ( Seed),     This->schedule (Schedule_selector (Maingamelayer::getcardnumber), 1.0),     return true;26}27 maingamelayer::getcardnumber void (float dt) {     randomnumber = Ccarddispatcher::sharedispatcher () GetRandomNumber ();     Cclog ("%d", randomnumber); 31}

Then debug, success.

So, set the seed position to put the loop outside .....

Cocos2d-x on the problem of obtaining random numbers