C ++ - 捕获内置＆＃34;除以零＆＃34;例外

Question

我正在编写一个前缀计算器程序，由于前缀的结构方式，很难处理除以零。幸运的是，如果C ++除以零，它就有一个内置异常。我如何处理以下异常，以便它向控制台返回个性化消息而不是弹出这个窗口？当我被ZERO分开时，我需要这个窗口不会弹出。

template<class T>
T PrefixCalculator<T>::eval(istringstream& input) {  //this function needs to throw an     exception if there's a problem with the expression or operators
char nextChar = input.peek();

//handles when invalid characters are input
if(nextChar > '9' || nextChar == '.' || nextChar == ',' || nextChar < '*' &&      nextChar != 'ÿ') {
    throw "invalidChar";
}

//this while loop skips over the spaces in the expression, if there are any
while(nextChar == ' ') {
    input.get();    //move past this space
    nextChar = input.peek(); //check the next character
}

if(nextChar == '+') {
    input.get();    //moves past the +
    return eval(input) + eval(input);   //recursively calculates the first expression, and adds it to the second expression, returning the result
}

/***** more operators here ******/
if(nextChar == '-') {
    input.get();
    return eval(input) - eval(input);
}

if(nextChar == '*') {
    input.get();
    return eval(input) * eval(input);
}

if(nextChar == '/') {
    input.get();

    return eval(input) / eval(input);
}

/******  BASE CASE HERE *******/
//it's not an operator, and it's not a space, so you must be reading an actual  value (like '3' in "+ 3 6".  Use the >> operator of istringstream to pull in a T value!
input>>nextChar;
T digit = nextChar - '0';

return digit;
//OR...there's bad input, in which case the reading would fail and you should throw an exception
}

template<class T>
void PrefixCalculator<T>::checkException() {
if(numOperator >= numOperand && numOperator != 0 && numOperand != 0) {
    throw "operatorError";
}
if(numOperand > numOperator + 1) {
    throw "operandError";
}
}

Answer 1

您用来解释复杂操作的符号，并不会改变您执行低级别操作的方式 - 例如除法。在代码的某处，您必须执行一个简单的x/y，在那个地方，当您知道自己将要分裂时，请检查0：

if(y==0)
   // your error handling goes here, maybe simple y=1
stack.pushBack(x/y);

请注意，在C ++中，除以0并不是一个例外。引用Stroustrup - 语言的创造者：

  

＆＃34;假设低级事件（例如算术溢出和除以零）由专用的低级机制而不是异常处理。这使C ++能够在算术时匹配其他语言的行为。它还避免了在严重流水线架构上出现的问题，其中除以零之类的事件是异步的。＆＃34;

在你的情况下：

if(nextChar == '/') {
    input.get();
    T x = eval(input);
    T y = eval(input);

    if(!y) handlingTheVeryDifficultSituation();
    return x/y;
}