英文:
Efficiency Comparison: (condition1 && condition2) vs. if (condition1) { if (condition2) }
问题
你好，开发者们，
我有一个关于条件语句中两种不同方法效率的问题。我正在尝试确定以下两种情况中哪一种选项更快：
1.使用逻辑运算符&&将两个条件组合在单个if语句中：if (condition1 && condition2)
2.利用嵌套的if语句分别评估条件：
if (condition1) {
if (condition2) {
// 仅当两个条件都为真时执行的代码块
}
}
我的目标是优化我的代码，确保在执行时间方面使用最有效的方法。因此，我将非常感谢您对这两种替代方案的性能影响提供见解。
具体来说，我对理解在计算开销、短路评估行为和总体执行速度方面可能存在的潜在差异感兴趣。
如果您对这个话题有任何经验或知识，或者如果您可以指向相关资源，我将不胜感激。提前感谢您的帮助！
英文:
Hello fellow developers,
I have a question regarding the efficiency of two different approaches in conditional statements. I am trying to determine which option is faster between the following two scenarios:
1.Using the logical operator && to combine two conditions within a single if statement: if (condition1 && condition2)
2.Utilizing nested if statements to evaluate the conditions separately:
if (condition1) {
if (condition2) {
// Code block executed if both conditions are true
}
}
My goal is to optimize my code and ensure that I am using the most efficient approach in terms of execution time. Therefore, I would greatly appreciate your insights on the performance implications of these two alternatives.
Specifically, I am interested in understanding any potential differences in terms of computational overhead, short-circuit evaluation behavior, and overall execution speed.
If you have any experience or knowledge regarding this topic, or if you can point me to relevant resources, I would be grateful for your assistance. Thank you in advance!
答案1
得分: 8
它没有任何区别。&& 运算符是短路的，意味着如果左侧是 false，右侧不会被执行。
通过短路，if (A && B) ... 的工作方式与 if (A) if (B) ... 完全相同，编译器知道这一点。
英文:
It doesn't make any difference. The && operator is short-circuiting, meaning that the right-hand side isn't executed if the left-hand side is false.
With the short-circuiting, if (A && B) ... works exactly like if (A) if (B) ..., and the compiler knows this.
答案2
得分: 1
-
如果您正在寻求（微小的）优化，您有三个主要选项用于
if (option1 && option2) {...}： -
首先检查
option1，然后根据需要检查option2。 -
首先检查
option2，然后根据需要检查option1。 -
计算
option1和option2，然后检查是否为true。
如果其中一个选项很昂贵，可以在第二个位置检查它（如果其他选项为 false，则不必检查它）：
if (cheapOption && expensiveOption) { ... }
请注意，嵌套的 if 等同于 &&，不会提高性能。
如果您有两个廉价的选项，但仍然寻求优化，可以尝试使用 & 而不是 &&，以摆脱额外的 if（以及可能与 CPU 分支预测有关的问题）：
if (cheapOption1 & cheapOption2) { ... }
英文:
If you are looking for (micro) optimization you have three main options for if (option1 && option2) {...}:
- Check
option1, and thenoption2if required. - Check
option2, and thenoption1if required. - Compute both
option1andoption2and then check fortrue.
If one of option is expensive, check it second (if other option is false you don't have to check it):
if (cheapOption && expensiveOption) { ... }
Please note, that nested if equals to && and doesn't improve performance.
In case you have two cheap options and you still look for optimization, try & instead of && in order to get
rid of extra if (and possible problems with CPU branch prediction):
if (cheapOption1 & cheapOption2) { ... }
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