memory error

This is a discussion on memory error within the C++ Programming forums, part of the General Programming Boards category; Hi, Currently working through Stroustrup - Programming Principles and having problem with a particular function he advises to use: Code: ...

  1. #1
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    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.

  2. #2
    C++ Witch laserlight's Avatar
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    That should be expected: the function apparently deliberately does not catch the exception thrown.
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    Because you're throwing an exception...? Maybe you should try reading up on exceptions and exception handling before continuing?

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    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

  5. #5
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    However, the code above is taken directly from Stroustrup's book
    most likely, you've missed something.

    Damn Stroustrup!
    sacrilege!

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    Quote Originally Posted by m37h0d View Post
    most likely, you've missed something.



    sacrilege!
    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???

  7. #7
    Jack of many languages Dino's Avatar
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    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..."?
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    Quote Originally Posted by Dino View Post
    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.

  9. #9
    Jack of many languages Dino's Avatar
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    You'll have to handle the exception and print the error string.
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  10. #10
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    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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    Quote Originally Posted by m37h0d View Post
    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.
    Are you saying that when runtime_error is thrown, that's what causes the message box and subsequent error?

  12. #12
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    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.

  13. #13
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    Quote Originally Posted by darren78 View Post
    Are you saying that when runtime_error is thrown, that's what causes the message box and subsequent error?
    yes, exactly.

    also, this:

    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
    Last edited by m37h0d; 10-26-2009 at 02:19 PM.

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    Quote Originally Posted by m37h0d View Post
    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.

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    (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++

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