Terminate() inside constructor

This is a discussion on Terminate() inside constructor within the C++ Programming forums, part of the General Programming Boards category; I'm writing a reusable class. The constructor (declared explicit) makes several checks on the std::string passed as an argument. In ...

  1. #1
    (?<!re)tired Mario F.'s Avatar
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    Terminate() inside constructor

    I'm writing a reusable class. The constructor (declared explicit) makes several checks on the std::string passed as an argument.
    In case of a malformed string it throws an exception. Several errors are possible and each provides its own throw. The throws are using the standard library objects declared in stdexcept.

    After all checks are done, it then proceeds to fill in some of its data members.

    The whole error checking section is contained inside a try-catch block.
    The catch blocks simply output the error message through std::cerr and then... I call terminate().

    And this is what is worrying me, as this means any constructors for any objects created so far on the code (some of which could be dynamically allocated objects of other types) exit abnormally without their destructors being called. Using my class would mean that during the coding and testing process, a programmer could be faced with innumerous memory leaks.

    How should I approach this? Should I simply throw and expect the class user to set try-catch blocks on their code (If I still want to output the error message I can simply cerr it and rethrow)?

    On the event I want to actually exit on the constructor, how can I output the error message, and terminate the program safely?
    Last edited by Mario F.; 07-13-2006 at 07:36 PM.
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

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    Well if you are actually exiting the program, then all the memmory allocated to the program will be returned to the OS. Atleast with recent OS's. In such a case, calling delete on all alocated memmory is more a good stile thing.

    Old OS's (pre Windows 98 I think) actually did have a problem if memmory was not explisidly freed when the program ends.
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

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    that sounds like a good use for auto_ptr (or was it autoptr?) - anyway its part of the stl.
    it simply wraps a pointer, and deletes the object when the destructor of the autopointer is called.

    note that when a constructor of a class exits due to a throw, all members are destroyed - but the destructor of the class where the ctor failed won't be called.
    so since all members are destroyed, having all pointers to dynamically created objects wrapped by the auto pointer, the memory will be deallocated safely.
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  4. #4
    (?<!re)tired Mario F.'s Avatar
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    Ok... maybe I not interpretating correctly what I read about the terminate function...

    Code:
    int main() {
    
    /*... lots of stuff is coded here including allocated objects ... */
    
    LINE 1543: myclass obj("bad string"); //Bang! Constructor throws and catches. Inside the catch
                                               // block, I output the error message and call terminate()
    }
    Will the objects declared before line 1543 call their destructors?
    Last edited by Mario F.; 07-13-2006 at 08:07 PM.
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

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    well when the program exits, the operating system should clean up all associated memory.
    why the need to call terminate? wouldnt it suffice either to throw some other exception - or return some value - and let the variables go out of scope?

    edit: i doubt that terminate has a chance to clean up anything. by default it calls abort, and that simply kills the process (afaik). thus the destructors won't be called, since the process terminates, before they would be called automatically by going out of scope.
    Last edited by Raven Arkadon; 07-13-2006 at 08:17 PM.
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  6. #6
    (?<!re)tired Mario F.'s Avatar
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    On unhandled exception cases g++ 3.4.2 only outputs a laconic message. I need to hint the coder as to what caused the exception, hence the need to catch the error and std::cerr it.

    However, I see your point... you suggest I rethrow?
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

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    ya, i would rethrow
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    If I don't use try...catch on new, and it threw a std::bad_alloc, which totalled my carefully written application, that's my own fault. I wouldn't call Bjarne and complain that he didn't write a handler into the implementation and call abort.

    Come to think of it, you can just throw the error message with the whole package and all the works and let the user handle/print/log it at a convenient time.

    This is my personal opinion, but you're writing a class, not an application. A user might create an application using other classes with numerous dependencies which happens to include your class. Or a server or other critical system device that must handle errors silently and never close. Error handling should be build into the user interface so that the user can decide where, how and when to handle any messages generated by your class.
    Last edited by jafet; 07-14-2006 at 04:01 AM.
    Code:
    #include <stdio.h>
    
    void J(char*a){int f,i=0,c='1';for(;a[i]!='0';++i)if(i==81){
    puts(a);return;}for(;c<='9';++c){for(f=0;f<9;++f)if(a[i-i%27+i%9
    /3*3+f/3*9+f%3]==c||a[i%9+f*9]==c||a[i-i%9+f]==c)goto e;a[i]=c;J(a);a[i]
    ='0';e:;}}int main(int c,char**v){int t=0;if(c>1){for(;v[1][
    t];++t);if(t==81){J(v[1]);return 0;}}puts("sudoku [0-9]{81}");return 1;}

  9. #9
    (?<!re)tired Mario F.'s Avatar
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    Okies. Thanks everyone.
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

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