memory error

Hi,

Currently working through Stroustrup - Programming Principles and having problem with a particular function he advises to use:

Code:

---

#include <iostream>

using namespace std;

void error(const string& s)
{
        throw runtime_error(s);
}



int main()

{
        cout << "Please enter an expression (we can handle +, -, / or *): ";
        int lval = 0;
        int rval;
        char op;
        cin >> lval;
        if(!cin) error("no first operand");

        while(cin>>op){
                cin >> rval;
                if(!cin) error("no second operand");
                switch(op){
                        case '+':
                                lval+=rval;
                                break;
                        case '-':
                                lval-=rval;
                                break;
                        case '*':
                                lval *=rval;
                                break;
                        case '/':
                                lval /= rval;
                                break;
                        default:
                                cout << "Result: " << lval << '\n';
                               
                }
        }
        error ("bad expression");
        system("pause");
                                return 0;
       


}

---

When I enter bad input to call the error function I get this message: Unhandled exception at 0x761c42eb in Accelerated C++.exe: Microsoft C++ exception: std::runtime_error at memory location 0x0022fb54..

Anybody any idea why?

Thanks.

That should be expected: the function apparently deliberately does not catch the exception thrown.

Because you're throwing an exception...? Maybe you should try reading up on exceptions and exception handling before continuing?

I have done a little reading on exception handling and am aware of try, throw, catch etc. However, the code above is taken directly from Stroustrup's book?

Also when I try to use the calculator with the code above, it doesnt work properly, for example when i type 2+2 and then keep pressing enter nothing happens. Only when I type another integer without and operator does it give me the result!!!! Damn Stroustrup! Anybody any ideas?

Thanks

Quote:

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However, the code above is taken directly from Stroustrup's book

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most likely, you've missed something.

Quote:

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Damn Stroustrup!

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sacrilege!

Quote:

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Originally Posted by m37h0d

most likely, you've missed something.



sacrilege!

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Ha.....code is definately correct, except for the error function which Stroustrup has included in his own header file. He has used:

Code:

---

inline void error(const string& s)
{
        throw runtime_error(s);
}

---

According to Stroustrup that is meant to disguise the throw? The function call is as above in my original code???

What are you expecting to happen?

Does he have a small disclaimer at the front of the book, something to the effect of "not all examples show full error handling logic..."?

Quote:

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Originally Posted by Dino

What are you expecting to happen?

Does he have a small disclaimer at the front of the book, something to the effect of "not all examples show full error handling logic..."?

---

I was expecting it to return an error string. Or at the very least not make the program unworkable.

I can't see any disclaimer either.

You'll have to handle the exception and print the error string.

on closer inspection...it appears to be doing exactly what it's intended to. stop freaking out because it's not doing what you expect it to and try to understand what it does.

Quote:

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Originally Posted by m37h0d

on closer inspection...it appears to be doing exactly what it's intended to. stop freaking out because it's not doing what you expect it to and try to understand what it does.

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Are you saying that when runtime_error is thrown, that's what causes the message box and subsequent error?

Doing a bit of research it is apparently the way that exceptions are handled by the debugger. A little further research is required I think....thanks for the response so far guys.

Quote:

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Originally Posted by darren78

Are you saying that when runtime_error is thrown, that's what causes the message box and subsequent error?

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yes, exactly.

also, this:

Quote:

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Also when I try to use the calculator with the code above, it doesnt work properly, for example when i type 2+2 and then keep pressing enter nothing happens. Only when I type another integer without and operator does it give me the result!!!! Damn Stroustrup! Anybody any ideas?

---

doesn't at all match with the apparent usage case.

study the code; particularly, try to understand the program execution flow.

like i said...you missed something ;)

Quote:

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Originally Posted by m37h0d

yes, exactly.

also, this:



doesn't at all match with the apparent usage case.

study the code; particularly, try to understand the program execution flow.

like i said...you missed something ;)

---

Thanks for the responses.....I understand now.

Cheers.

(1) That code is not copied exactly: system("pause"); is never used in PPP
(2) The main() for that example has a try block
(3) You can find all the code for the book at Stroustrup: Programming -- Principles and Practice Using C++

Wow.

Quote:

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Originally Posted by bjarne

(1) That code is not copied exactly: system("pause"); is never used in PPP
(2) The main() for that example has a try block
(3) You can find all the code for the book at Stroustrup: Programming -- Principles and Practice Using C++

---

Hi,

Thanks for the response,and in answer:

1. I know this is not used in the book, however I prefer it to keep_window_open(), and this would not affect the output
2. The code in the book does not have a try block. (page 178)
3. Thanks for the link, I will take a look later.

Quote:

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Originally Posted by darren78

2. The code in the book does not have a try block. (page 178)

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Maybe the website has the corrected code.

Quote:

---

Originally Posted by darren78

Hi,

Thanks for the response,and in answer:

1. I know this is not used in the book, however I prefer it to keep_window_open(), and this would not affect the output
2. The code in the book does not have a try block. (page 178)
3. Thanks for the link, I will take a look later.

---

Hi Bjarne

I have downloaded the code, and that works perfectly. Thank you. It is however different to the book I have. Were their different versions released?

And on a good note, it is by far the best beginners book I have used. Very clear with good examples and lots of excercises to practise with!! Much prefer it to APP.