C：你如何来模拟一个“例外”？ [英] C : How do you simulate an 'exception'?

问题描述

我来自一个C＃背景，但我目前学习C。在C＃中，当一个人想要的信号已发生错误，则抛出异常。但是你怎么用C呢？

I come from a C# background, but I'm learning C at the moment. In C#, when one wants to signal that an error has occurred, you throw an exception. But what do you do in C?

例如说，你有推和弹出函数的栈。什么是信号堆栈一个弹出期间是空的最好方法？你从函数返回什么？

Say for example you have a stack with push and pop functions. What is the best way to signal that the stack is empty during a pop ? What do you return from that function?

double pop(void)
{
    if(sp > 0)
        return val[--sp];
    else {
        printf("error: stack empty\n");
        return 0.0;
    }
}

K＆放大器;从第77页（S R 例子的 code时上部的）返回一个 0.0 。但是，如果用户按下一个 0.0 早前在栈上，你怎么知道堆栈是否为空，或者是否返回正确的价值？

K&R's example from page 77 (code above) returns a 0.0. But what if the user pushed a 0.0 earlier on the stack, how do you know whether the stack is empty or whether a correct value was returned?

推荐答案

在C异常类似的行为是通过的setjmp /完成longjmp的。但是，你真的想在这里什么是错误code。如果所有的值都是潜在的可回收，那么你可能想在out参数为指针，并用它来返回值，像这样：

Exception-like behavior in C is accomplished via setjmp/longjmp. However, what you really want here is an error code. If all values are potentially returnable, then you may want to take in an out-parameter as a pointer, and use that to return the value, like so:

int pop(double* outval)
{
        if(outval == 0) return -1;
        if(sp > 0)
                *outval = val[--sp];
        else {
                printf("error: stack empty\n");
                return -1;
        }
        return 0;
}

不理想，很明显，但这样是C的局限性。

Not ideal, obviously, but such are the limitations of C.

另外，如果你走这条路，你可能要定义符号常量为你的错误codeS（或者使用一些的the标准的人的），使用户可以区分堆空和你给了我一个空指针，笨蛋。

Also, if you go this road, you may want to define symbolic constants for your error codes (or use some of the standard ones), so that a user can distinguish between "stack empty" and "you gave me a null pointer, dumbass".

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