Question

我正在为我的游戏设置音效音量。我希望音量从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并继续倒计时。请告诉我有什么问题。感谢

-(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"]);
}

仅点击“降低音量”按钮，这是我的日志输出：

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

修改

更改为＆gt; =和＆lt; =（分别）具有以下输出：

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

Answer 1

浮点运算并不精确 - 从1.0开始减去0.1十次并不一定能给出0.0。有关详细信息，请阅读经典论文What Every Computer Scientist Should Know About Floating-Point Arithmetic。

通过避免严格的相等比较（例如，使用[0.0, 1.0]或>=而不是<=，您可以通过将值更改为==来解决此问题。），或者 - 理想情况下 - 通过简单地将体积存储在0到10之间的整数，并在需要的地方除以10.0。

浮点数，负零点？

1 个答案: