当代码流是这样的:
if(check())
{
...
...
if(check())
{
...
...
if(check())
{
...
...
}
}
}
我通常看到这种方法可以避免上述混乱的代码流:
do {
if(!check()) break;
...
...
if(!check()) break;
...
...
if(!check()) break;
...
...
} while(0);
有什么更好的方法可以避免这种工作/黑客，从而使其成为更高级别(行业级别)的代码?
任何跳出盒子的建议都是欢迎的!
当前回答
Try to extract the code into a separate function (or perhaps more than one). Then return from the function if the check fails. If it's too tightly coupled with the surrounding code to do that, and you can't find a way to reduce the coupling, look at the code after this block. Presumably, it cleans up some resources used by the function. Try to manage these resources using an RAII object; then replace each dodgy break with return (or throw, if that's more appropriate) and let the object's destructor clean up for you. If the program flow is (necessarily) so squiggly that you really need a goto, then use that rather than giving it a weird disguise. If you have coding rules that blindly forbid goto, and you really can't simplify the program flow, then you'll probably have to disguise it with your do hack.
其他回答
你可以使用一个简单的bool变量的延续模式:
bool goOn;
if ((goOn = check0())) {
...
}
if (goOn && (goOn = check1())) {
...
}
if (goOn && (goOn = check2())) {
...
}
if (goOn && (goOn = check3())) {
...
}
这个执行链将在checkN返回false时停止。由于&&操作符短路，将不再执行进一步的检查…()调用。此外，优化编译器足够聪明，可以识别将goOn设置为false是单行道，并为您插入缺少的goto结尾。因此，上面代码的性能将与do/while(0)相同，只是对其可读性没有严重的影响。
如果你的代码有一个很长的If ..else If ..else语句块，你可以尝试在函子或函数指针的帮助下重写整个块。这可能并不总是正确的解决方案，但通常是正确的。
http://www.cprogramming.com/tutorial/functors-function-objects-in-c++.html
I'm adding an answer for the sake of completeness. A number of other answers pointed out that the large condition block could be split out into a separate function. But as was also pointed out a number of times is that this approach separates the conditional code from the original context. This is one reason that lambdas were added to the language in C++11. Using lambdas was suggested by others but no explicit sample was provided. I've put one in this answer. What strikes me is that it feels very similar to the do { } while(0) approach in many ways - and maybe that means it's still a goto in disguise....
earlier operations
...
[&]()->void {
if (!check()) return;
...
...
if (!check()) return;
...
...
if (!check()) return;
...
...
}();
later operations
我不是c++程序员，所以我不会在这里写任何代码，但到目前为止还没有人提到面向对象的解决方案。下面是我的猜测:
拥有一个通用接口，该接口提供了一个方法来评估单个条件。现在，您可以在包含有问题的方法的对象中使用这些条件的实现列表。遍历列表并计算每个条件，如果其中一个条件失败，可能会提前爆发。
这样的设计很好地遵循了开/闭原则，因为在初始化包含相关方法的对象时，可以很容易地添加新的条件。您甚至可以向接口添加第二个方法，该方法用于条件评估，返回条件的描述。这可以用于自文档系统。
但是，缺点是由于使用了更多的对象和遍历列表，所涉及的开销稍微多一些。
类似于dasblinkenlight的答案，但避免了if语句中的赋值，这可能会被代码评审员“修复”:
bool goOn = check0();
if (goOn) {
...
goOn = check1();
}
if (goOn) {
...
goOn = check2();
}
if (goOn) {
...
}
...
当一个步骤的结果需要在下一步之前检查时，我使用这种模式，这与所有检查都可以在前面用一个大if(check1() && check2()…类型的模式。
