c++ - 在C++中使用堆栈评估后缀表达式

好的，我已经用后缀符号表示了，并且我正在发送一个字符串变量，该变量将具有后缀表示法，例如：5 15 2 * +
这是我的代码：

int evaluatePostFix(string postfix_expression){
//Create a new stack
stack<int> theStack;
//Loops while the postfix expression string still contains values
while(postfix_expression.length()>=1){
    //Loops on a number an whitespace
    while(isdigit(postfix_expression.at(0)) || isspace(postfix_expression.at(0))){
        //Holds a number that is above two digits to be added to the stack
        string completeNum;
        if(isdigit(postfix_expression.at(0))){
            //Add the digit so it can become a full number if needed
            completeNum+=postfix_expression.at(1);
        }
        else {
            //Holds the integer version of completeNum
            int intNum;
            //Make completeNum an int
            intNum=atoi(completeNum.c_str());
            //push the number onto the stack
            theStack.push(intNum);
        }
        //Check to see if it can be shortened
        if(postfix_expression.length()>=1){
            //Shorten the postfix expression
            postfix_expression=postfix_expression.substr(1);
        }
    }
    //An Operator has been found
    while(isOperator(postfix_expression.at(0))){
        int num1, num2;
        char op;
        //Grabs from the top of the stack
        num1=theStack.top();
        //Pops the value from the top of the stack - kinda stupid how it can return the value too
        theStack.pop();
        //Grabs the value from the top of the stack
        num2=theStack.top();
        //Pops the value from the top of the stack
        theStack.pop();
        //Grab the operation
        op=postfix_expression.at(0);
        //Shorten the postfix_expression
        postfix_expression=postfix_expression.substr(1);
        //Push result onto the stack
        theStack.push(Calculate(num1,num2, op));
    }
}
return theStack.top();

}

我得到的错误是“不可延迟的Deque迭代器”

我可以就此错误获得的任何帮助将不胜感激。
顺便说一句，我已经有两年没有使用C ++了，所以我有点生锈。

最佳答案

如果您通过逐步调试通过告诉我们哪一行导致了错误，那会更容易。但是，我认为我可能已经发现了错误。

在这段代码中

if(isdigit(postfix_expression.at(0))){
    //Add the digit so it can become a full number if needed
    completeNum+=postfix_expression.at(1);
}

您要求postfix_expression.at（1），而无需检查该元素是否存在。由于没有检查，您可能正在访问错误的内存位置。

关于c++ - 在C++中使用堆栈评估后缀表达式，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/7883858/