请教一个随机数的问题,谢谢

jlu_sh 2005-03-28 09:26:57
在程序中按照以下方式产生的随机数没有问题:
#include <stdlib.h>
#include <stdio.h>
#include <time.h>

void main( void )
{
int i;

/* Seed the random-number generator with current time so that
* the numbers will be different every time we run.
*/
srand( (unsigned)time( NULL ) );

/* Display 10 numbers. */\

int tmp;
double tempdouble;

for( i = 0; i < 1000;i++ )
{
tmp = rand();
printf( " %6d\n", tmp );
tempdouble = ((double)tmp)/RAND_MAX;

printf("tempdouble =%10.24f\n", tempdouble);
}

}
但是换成以下的程序
...
srand((unsigned)time( NULL));
while(pointCount < m_triangleNum)
{
float r1 = ((float)(rand()))/RAND_MAX;
TRACE("The m_index is %10.24f\n", r1);
...
}
的时候，在调试的时候出现的随机数都是一样的，如下所示：
The m_index is 0.505325479903561470000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
The m_index is 0.152867213965269950000000
...(后面的数据都是一样的)
为什么在这里产生的随机数就不是随机的了？急盼您的回答，万分感谢！
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pp_ipr 2005-03-28
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能不能贴出产生一致随机数的完整代码段？
xenke 2005-03-28
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我运行时是随机的,你找找其他方面的原因
jlu_sh 2005-03-28
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将float r1 = ((float)(rand()))/RAND_MAX;改成double r1 = ((double)(rand()))/RAND_MAX;产生的数据还是一样的。谢谢！
jlu_sh 2005-03-28
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我也认为Sleep（）不好，但是即使Sleep（）了，产生的数据还是不是随机的数，看上去更像一个递增的序列。郁闷
pp_ipr 2005-03-28
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改成srand((unsigned)GetTickCount());试试？
pp_ipr 2005-03-28
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奇怪...
难道是硬件原因
cut9 2005-03-28
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靠Sleep不好。
jlu_sh 2005-03-28
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按照lzd(活着便精彩)的提议,我修改了一下(我的程序Sleep(6)),产生的数据如下:
The m_index is 0.470412305063020730000000
The m_index is 0.472090823084200580000000
The m_index is 0.472914822840052480000000
The m_index is 0.473586230048524400000000
The m_index is 0.474288155766472370000000
The m_index is 0.474990081484420290000000
The m_index is 0.475600451673940270000000
The m_index is 0.476302377391888190000000
The m_index is 0.476973784600360110000000
The m_index is 0.477675710318308080000000
The m_index is 0.478774376659443950000000
The m_index is 0.479476302377391860000000
The m_index is 0.480178228095339830000000
The m_index is 0.480880153813287750000000
The m_index is 0.481582079531235720000000
The m_index is 0.482284005249183630000000
The m_index is 0.482955412457655550000000
The m_index is 0.483565782647175530000000
The m_index is 0.484267708365123450000000
The m_index is 0.485366374706259370000000
The m_index is 0.486068300424207290000000
The m_index is 0.486739707632679210000000
The m_index is 0.487441633350627180000000
The m_index is 0.488143559068575090000000
The m_index is 0.488845484786523010000000
The m_index is 0.489547410504470980000000
The m_index is 0.490249336222418900000000
The m_index is 0.490951261940366810000000
The m_index is 0.491622669148838790000000
The m_index is 0.492233039338358710000000
The m_index is 0.492934965056306630000000
The m_index is 0.493636890774254600000000
The m_index is 0.494338816492202520000000
The m_index is 0.495040742210150430000000
The m_index is 0.495712149418622410000000
The m_index is 0.496322519608142330000000
The m_index is 0.497024445326090250000000
The m_index is 0.497726371044038220000000
The m_index is 0.498428296761986130000000
The m_index is 0.499099703970458110000000
The m_index is 0.499801629688406020000000
The m_index is 0.500411999877925950000000
The m_index is 0.501113925595873870000000
The m_index is 0.501815851313821780000000
The m_index is 0.502487258522293810000000
The m_index is 0.503585924863429680000000
The m_index is 0.504287850581377590000000
The m_index is 0.504898220770897520000000
The m_index is 0.505600146488845440000000
The m_index is 0.506302072206793460000000
The m_index is 0.506973479415265380000000
The m_index is 0.507675405133213300000000
The m_index is 0.508377330851161210000000
The m_index is 0.508987701040681140000000
The m_index is 0.509689626758629060000000
The m_index is 0.510361033967101090000000
The m_index is 0.511062959685049000000000
The m_index is 0.511764885402996920000000
...
这个看上去也不是一个随机的数列啊。十分感谢！
jlu_sh 2005-03-28
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谢谢cut9(切瓜玩)，我现在只需要产生0~1之间的随机数，利用这个随机数去提取三维模型中的一些特征点。因为这个随机数产生的不好，导致最后提取出来的特征点都集中在某一个固定的区域，根本反应不出来三维模型的特征。你的那个能产生出0~1的随机数么？
cut9 2005-03-28
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我自己写过一个随机发生器,为的是产生密码用的。因为srand的种子依赖于系统时间，
再说种子确定了，那么那串随机数就确定了，这样产生密码不安全。
要不我给你我的？
jlu_sh 2005-03-28
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不会吧,在我这里怎么会是这样呢,我的CPU是奔四的呀,郁闷!还是很感谢!
cut9 2005-03-28
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难道srand跟CPU有关系吗？你是什么CPU啊
cut9 2005-03-28
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你的程序在我这儿运行，结果很好: (100个随机数)


The m_index is 0.443952757347331140000000
The m_index is 0.329264198736533730000000
The m_index is 0.369151890621662040000000
The m_index is 0.600970488601336730000000
The m_index is 0.033997619556260870000000
The m_index is 0.300088503677480410000000
The m_index is 0.454298532059694230000000
The m_index is 0.690664387951292480000000
The m_index is 0.716208380382702070000000
The m_index is 0.441053498947111430000000
The m_index is 0.345927304910428170000000
The m_index is 0.441236610003967410000000
The m_index is 0.080477309488204599000000
The m_index is 0.822443311868648390000000
The m_index is 0.812280648213141280000000
The m_index is 0.111239967040009770000000
The m_index is 0.162297433393353060000000
The m_index is 0.404828028199102740000000
The m_index is 0.270729697561571110000000
The m_index is 0.050294503616443373000000
The m_index is 0.606707968382824150000000
The m_index is 0.671681875057222210000000
The m_index is 0.515854365672780530000000
The m_index is 0.641102328562273010000000
The m_index is 0.467268898586993000000000
The m_index is 0.357219153416547140000000
The m_index is 0.159611804559465300000000
The m_index is 0.102755821405682540000000
The m_index is 0.421033356730857290000000
The m_index is 0.926847132786034700000000
The m_index is 0.816278572954496910000000
The m_index is 0.061799981688894313000000
The m_index is 0.680837427900021330000000
The m_index is 0.965178380687887190000000
The m_index is 0.562364574114200270000000
The m_index is 0.296761986144596700000000
The m_index is 0.386028626361888500000000
The m_index is 0.128971221045564130000000
The m_index is 0.703543198950163260000000
The m_index is 0.563249610889004160000000
The m_index is 0.752891628772850760000000
The m_index is 0.820581682790612500000000
The m_index is 0.379070406201361120000000
The m_index is 0.904843287453840790000000
The m_index is 0.766319772942289480000000
The m_index is 0.238227484969634080000000
The m_index is 0.035615100558488724000000
The m_index is 0.356944486831263170000000
The m_index is 0.693441572313608260000000
The m_index is 0.959837641529587730000000
The m_index is 0.301431318094424250000000
The m_index is 0.449476607562486640000000
The m_index is 0.201086458937345500000000
The m_index is 0.715872676778466110000000
The m_index is 0.292062135685293160000000
The m_index is 0.414288766136661880000000
The m_index is 0.357799005096591070000000
The m_index is 0.508285775322733220000000
The m_index is 0.879146702475051110000000
The m_index is 0.504287850581377590000000
The m_index is 0.301889095736564250000000
The m_index is 0.731192968535416710000000
The m_index is 0.953062532425916320000000
The m_index is 0.329844050416577660000000
The m_index is 0.856837672048097130000000
The m_index is 0.449781792657246600000000
The m_index is 0.211340678121280550000000
The m_index is 0.619403668324839060000000
The m_index is 0.875179296243171480000000
The m_index is 0.493758964812158590000000
The m_index is 0.503341776787621710000000
The m_index is 0.309640797143467540000000
The m_index is 0.592059083834345580000000
The m_index is 0.521286660359507990000000
The m_index is 0.263069551683095810000000
The m_index is 0.372478408154545750000000
The m_index is 0.769981994079409150000000
The m_index is 0.710257271034882680000000
The m_index is 0.061006500442518388000000
The m_index is 0.284371471297341860000000
The m_index is 0.915738395336771700000000
The m_index is 0.232306894131290630000000
The m_index is 0.806573686941129740000000
The m_index is 0.544480727561265860000000
The m_index is 0.350657673879207770000000
The m_index is 0.166661580248420680000000
The m_index is 0.631611072115237930000000
The m_index is 0.147831659901730390000000
The m_index is 0.416119876705221710000000
The m_index is 0.009430219428083133300000
The m_index is 0.987731559190649140000000
The m_index is 0.420239875484481330000000
The m_index is 0.594470046082949290000000
The m_index is 0.435132908108767980000000
The m_index is 0.986785485396893260000000
The m_index is 0.120090334788048950000000
The m_index is 0.827631458479567870000000
The m_index is 0.465987121189001150000000
The m_index is 0.517502365184484340000000
The m_index is 0.214575640125736270000000
lzd 2005-03-28
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while(pointCount < m_triangleNum)
{
sleep(1)
srand(timeGetTime() )
int a=rand()%xxx
}
jlu_sh 2005-03-28
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是不是跟TRACE（）语句有什么关系啊？
jlu_sh 2005-03-28
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不行啊，改成srand(timeGetTime())还是没有什么变化啊，但是在运行我贴的第一个程序的时候产生的数确实是随机数啊，不知道为什么一放到别的程序里面，运行的结果就不对了。谢谢！
lzd 2005-03-28
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srand(timeGetTime() )

改成这个..
jlu_sh 2005-03-28
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srand((unsigned)time( NULL));
while(pointCount < m_triangleNum)
{
float r1 = ((float)(rand()))/RAND_MAX;
TRACE("The m_index is %10.24f\n", r1);
float ran = r1 * totalArea;
int m_index = FindTriangleIndex(sumArea, ran);
//TRACE("The m_index is %d\n", m_index);
CTriangle sampleTriangle = m_triangleList.GetAt(m_triangleList.FindIndex(m_index));
if(pointCount == 0)
{
m_samplePoint.AddTail(*(sampleTriangle.GetSamplingPoint()));
}
else
{
m_samplePoint.InsertAfter(m_samplePoint.GetTailPosition(), *(sampleTriangle.GetSamplingPoint()));
}
pointCount++;
}

这就是产生一致随机数的完整代码,其他地方好像关系不大啊,我在调试的时候产生的随机数都不是真正的随机数,如果将断点设置在TRACE()语句上，一般产生5~6个相同的数后就会产生另一个差别不大的数，但是这个数又得重复5~6次才是下一个数，如果将F5按慢一点，产生的数倒是不同，但是还是不是随机的，看上去倒像一个递增的序列。如果将断点放在别的地方，在调试的时候输出的就像上面的那样了。谢谢！
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