c exception throwing std string

Question

I would like to throw an exception when my C   methods encounter something weird and can t recover  Is it OK to throw a std  string pointer   Here s what I was looking forward to doing   void Foo  Bar         if  QueryPerformanceTimer  amp m baz             throw new std  string  it s the end of the world              void Foo  Caller         try           this- gt Bar       should throw           catch std  string  caught       not quite sure the syntax is OK here            std  cout  lt  lt   Got    lt  lt  caught  lt  lt  std  endl

User · Answer

In addition to probably throwing something derived from std::exception you should throw anonymous temporaries and catch by reference:

void Foo::Bar(){
  if(!QueryPerformanceTimer(&m_baz)){
    throw std::string("it's the end of the world!");
  }
}

void Foo:Caller(){
  try{
    this->Bar();// should throw
  }catch(std::string& caught){ // not quite sure the syntax is ok here...
    std::cout<<"Got "<<caught<<std::endl;
  }
}

You should throw anonymous temporaries so the compiler deals with the object lifetime of whatever you're throwing - if you throw something new-ed off the heap, someone else needs to free the thing.
You should catch references to prevent object slicing

.

See Meyer's "Effective C++ - 3rd edition" for details or visit https://www.securecoding.cert.org/.../ERR02-A.+Throw+anonymous+temporaries+and+catch+by+reference

User · Answer

Yes  std  exception is the base exception class in the C   standard library   You may want to avoid using strings as exception classes because they themselves can throw an exception during use  If that happens  then where will you be   boost has an excellent document on good style for exceptions and error handling  It s worth a read

User · Answer

All these work    include  lt iostream gt  using namespace std     Good  because manual memory management isn t needed and this uses   less heap memory  or no heap memory  so this is safer if   used in a low memory situation void f     throw string  foo         Valid  but avoid manual memory management if there s no reason to use it void g     throw new string  foo         Best   Just a pointer to a string literal  so no allocation is needed    saving on cleanup  and removing a chance for an allocation to fail  void h     throw  foo      int main       try   f      catch  string s    cout  lt  lt  s  lt  lt  endl      try   g      catch  string  s    cout  lt  lt   s  lt  lt  endl  delete s      try   h      catch  const char  s    cout  lt  lt  s  lt  lt  endl      return 0      You should prefer h to f to g  Note that in the least preferable option you need to free the memory explicitly

User · Answer

A few principles    you have a std  exception base class  you should have your exceptions derive from it  That way general exception handler still have some information  Don t throw pointers but object  that way memory is handled for you    Example   struct MyException   public std  exception      std  string s     MyException std  string ss    s ss         MyException   throw          Updated    const char  what   const throw     return s c str           And then use it in your code   void Foo  Bar      if  QueryPerformanceTimer  amp m baz        throw MyException  it s the end of the world            void Foo  Caller      try      this- gt Bar      should throw    catch MyException amp  caught       std  cout lt  lt  Got   lt  lt caught what   lt  lt std  endl

User · Answer

Though this question is rather old and has already been answered  I just want to add a note on how to do proper exception handling in C  11   Use std  nested exception and std  throw with nested  Using these  in my opinion  leads to cleaner exception design and makes it unnecessary to create an exception class hierarchy   Note that this enables you to get a backtrace on your exceptions inside your code without need for a debugger or cumbersome logging  It is described on StackOverflow here and here  how to write a proper exception handler which will rethrow nested exceptions   Since you can do this with any derived exception class  you can add a lot of information to such a backtrace  You may also take a look at my MWE on GitHub  where a backtrace would look something like this   Library API  Exception caught in function  api function  Backtrace    Git mwe-cpp-exception src detail Library cpp 17   library function failed   Git mwe-cpp-exception src detail Library cpp 13   could not open file  nonexistent txt

User · Answer

Simplest way to throw an Exception in C      include  lt iostream gt  using namespace std  void purturb        throw  Cannot purturb at this time      int main         try          purturb              catch const char  msg           cout  lt  lt   We caught a message     lt  lt  msg  lt  lt  endl            cout  lt  lt   done       return 0      This prints   We caught a message  Cannot purturb at this time  done   If you catch the thrown exception  the exception is contained and the program will ontinue   If you do not catch the exception  then the program exists and prints    This application has requested the Runtime to terminate it in an unusual way   Please contact the application s support team for more information

User · Answer

It works  but I wouldn t do it if I were you   You don t seem to be deleting that heap data when you re done  which means that you ve created a memory leak   The C   compiler takes care of ensuring that exception data is kept alive even as the stack is popped  so don t feel that you need to use the heap   Incidentally  throwing a std  string isn t the best approach to begin with   You ll have a lot more flexibility down the road if you use a simple wrapper object   It may just encapsulate a string for now  but maybe in future you will want to include other information  like some data which caused the exception or maybe a line number  very common  that    You don t want to change all of your exception handling in every spot in your code-base  so take the high road now and don t throw raw objects

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