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社区首页 >问答首页 >浮点数，负零？

问浮点数，负零？
EN

Stack Overflow用户
提问于 2012-06-13 22:36:33
回答 1查看 259关注 0票数 0

我正在为我的游戏设置音效音量。我希望卷从0.0增加到1.0，增量为0.1。

然而，当它达到零时，我的日志反而告诉我它是-0.00000，并继续向下计数。请告诉我是怎么回事。谢谢

代码语言：javascript
复制
-(void)sfxUp{
     NSLog(@"SFX UP %f",[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]);
    if ([[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"] == 1.0f)
        return;
    [[NSUserDefaults standardUserDefaults]setFloat:([[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]+0.1f) forKey:@"sfx_volume"];
    [[NSUserDefaults standardUserDefaults]synchronize];
    [[SimpleAudioEngine sharedEngine] setEffectsVolume:[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]];
    NSLog(@"SFX UP %f",[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]);
}
-(void)sfxDown{
    NSLog(@"SFX DOWN %f",[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]);
    if ([[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"] == 0.0f)
        return;
    [[NSUserDefaults standardUserDefaults]setFloat:([[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]-0.1f) forKey:@"sfx_volume"];
    [[NSUserDefaults standardUserDefaults]synchronize];
    [[SimpleAudioEngine sharedEngine] setEffectsVolume:[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]];
     NSLog(@"SFX DOWN %f",[[NSUserDefaults standardUserDefaults]floatForKey:@"sfx_volume"]);
}

单击“音量下降”按钮，这是我的日志输出：

代码语言：javascript
复制
2012-06-13 18:32:25.067 Bomb Defuse[80558:1c403] SFX DOWN 1.000000
2012-06-13 18:32:25.068 Bomb Defuse[80558:1c403] SFX DOWN 0.900000
2012-06-13 18:32:25.385 Bomb Defuse[80558:1c403] SFX DOWN 0.900000
2012-06-13 18:32:25.386 Bomb Defuse[80558:1c403] SFX DOWN 0.800000
2012-06-13 18:32:25.623 Bomb Defuse[80558:1c403] SFX DOWN 0.800000
2012-06-13 18:32:25.624 Bomb Defuse[80558:1c403] SFX DOWN 0.700000
2012-06-13 18:32:25.873 Bomb Defuse[80558:1c403] SFX DOWN 0.700000
2012-06-13 18:32:25.874 Bomb Defuse[80558:1c403] SFX DOWN 0.600000
2012-06-13 18:32:26.116 Bomb Defuse[80558:1c403] SFX DOWN 0.600000
2012-06-13 18:32:26.140 Bomb Defuse[80558:1c403] SFX DOWN 0.500000
2012-06-13 18:32:26.346 Bomb Defuse[80558:1c403] SFX DOWN 0.500000
2012-06-13 18:32:26.348 Bomb Defuse[80558:1c403] SFX DOWN 0.400000
2012-06-13 18:32:26.605 Bomb Defuse[80558:1c403] SFX DOWN 0.400000
2012-06-13 18:32:26.608 Bomb Defuse[80558:1c403] SFX DOWN 0.300000
2012-06-13 18:32:26.835 Bomb Defuse[80558:1c403] SFX DOWN 0.300000
2012-06-13 18:32:26.838 Bomb Defuse[80558:1c403] SFX DOWN 0.200000
2012-06-13 18:32:27.068 Bomb Defuse[80558:1c403] SFX DOWN 0.200000
2012-06-13 18:32:27.069 Bomb Defuse[80558:1c403] SFX DOWN 0.100000
2012-06-13 18:32:27.319 Bomb Defuse[80558:1c403] SFX DOWN 0.100000
2012-06-13 18:32:27.338 Bomb Defuse[80558:1c403] SFX DOWN -0.000000
2012-06-13 18:32:27.630 Bomb Defuse[80558:1c403] SFX DOWN -0.000000
2012-06-13 18:32:27.640 Bomb Defuse[80558:1c403] SFX DOWN -0.100000
2012-06-13 18:32:27.946 Bomb Defuse[80558:1c403] SFX DOWN -0.100000
2012-06-13 18:32:27.947 Bomb Defuse[80558:1c403] SFX DOWN -0.200000
2012-06-13 18:32:28.170 Bomb Defuse[80558:1c403] SFX DOWN -0.200000
2012-06-13 18:32:28.172 Bomb Defuse[80558:1c403] SFX DOWN -0.300000
2012-06-13 18:32:28.414 Bomb Defuse[80558:1c403] SFX DOWN -0.300000
2012-06-13 18:32:28.416 Bomb Defuse[80558:1c403] SFX DOWN -0.400000
2012-06-13 18:32:28.641 Bomb Defuse[80558:1c403] SFX DOWN -0.400000
2012-06-13 18:32:28.643 Bomb Defuse[80558:1c403] SFX DOWN -0.500000
2012-06-13 18:32:28.869 Bomb Defuse[80558:1c403] SFX DOWN -0.500000
2012-06-13 18:32:28.870 Bomb Defuse[80558:1c403] SFX DOWN -0.600000
2012-06-13 18:32:29.301 Bomb Defuse[80558:1c403] SFX DOWN -0.600000
2012-06-13 18:32:29.303 Bomb Defuse[80558:1c403] SFX DOWN -0.700000
2012-06-13 18:32:29.584 Bomb Defuse[80558:1c403] SFX DOWN -0.700000
2012-06-13 18:32:29.586 Bomb Defuse[80558:1c403] SFX DOWN -0.800000

编辑：

更改为>=和<= (分别)具有以下输出：

代码语言：javascript
复制
2012-06-13 18:45:34.574 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:35.135 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:35.529 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:35.877 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.057 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.229 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.391 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.542 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.717 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:36.897 Bomb Defuse[80607:1c403] BG UP 1.000000
2012-06-13 18:45:37.599 Bomb Defuse[80607:1c403] BG DOWN1.000000
2012-06-13 18:45:37.602 Bomb Defuse[80607:1c403] BG DOWN0.900000
2012-06-13 18:45:38.431 Bomb Defuse[80607:1c403] BG DOWN0.900000
2012-06-13 18:45:38.491 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:38.617 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:38.951 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:39.125 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:39.479 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:39.908 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:40.399 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:40.624 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:40.841 Bomb Defuse[80607:1c403] BG DOWN-0.100000
2012-06-13 18:45:41.059 Bomb Defuse[80607:1c403] BG DOWN-0.100000
iphone
objective-c
ios
cocos2d-iphone
EN

回答 1

Stack Overflow用户

回答已采纳

发布于 2012-06-13 22:41:32

浮点运算是不准确的--从1.0开始，减去0.1 10次并不一定能给出精确的0.0。有关更多细节，请阅读经典报纸关于浮点算法，每个计算机科学家应该知道什么？。

在更改值时，可以将值限制为[0.0, 1.0]，避免严格的等式比较(例如，使用>=或<=而不是==)，或者--理想情况下--将卷存储为0到10之间的整数，并在需要时除以10.0。

票数 7
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/11024339

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