try-catch-throw

I don't really understand the advantages with the try-catch-throw statements. I took a look at msdn explanation of the statements and here's an example they've given:

Code:

int main() {
   char *buf;
   try {
      buf = new char[512];
      if( buf == 0 )
         throw "Memory allocation failure!";
   }
   catch( char * str ) {
      cout << "Exception raised: " << str << '\n';
   }
}

If I would have done the same thing I would have written:

Code:

int main() {
   char *buf;
   buf = new char[512];
   if (buf == 0) {
      cout << "Memory allocation failure!\n";
      cout << "Exception raised: " << str << '\n';
   }
}

I don't really se the difference and my is much more compact

Yeah. They repeat that kind of stuff on tutorials all over the web.
The hint is: forget about that throw.

Here's something a little better. http://www.gamedev.net/reference/art...article953.asp

Just keep reading past the first code you see.

The advantage is that exceptions automates the practice of bubbling up boolean returns. For example, this might be exception-less error checking code.

Code:

// Reads a person's age from the string database
// Returns 0 on error and sets errno
long getAge(char const * name) {
   char const * age_str;
   long age_num;

   age_str = database_lookup (name);
   if (errno) // Database lookup error
      return 0;

   if (age_str == NULL)
   { // Can't read a null value.
      errno = 1;
      return 0;
   }

   char * endptr;
   age_num = strtol (age_str, &endptr, 10);

   if (errno) // Range error
      return 0;

   if (*endptr != 0) // Didn't read the whole string, it's not an int
   {
      errno = 1;
      return 0;
   }
      
   return age_num;
}

The hope with exceptions is that we could change that to something like this...

Code:

// Reads a person's age from the string database
// Throws on err.
long getAge(char const * name) {
   char const * age_str = database_lookup (name);

   if (age_str == NULL)
   { // Can't read a null value.
      std::ostringstream err;
      err << "DB field USERS.AGE_STR contains NULL field for USERS.NAME = " << name;
      throw database_error (err.str());
   }

   return boost::lexical_cast<long>(age_str);
}

The second snippet handles all the same errors in all the same places, it's just all done under the hood.


The following links goe pretty into "Why exceptions are great" and how to properly use them, albeit light on examples.

http://www.parashift.com/c++-faq-lite/exceptions.html
http://www.scottcollins.net/articles/exceptions.html

Originally Posted by TriKri

Code:

int main() {
   char *buf;
   buf = new char[512];
   if (buf == 0) {
      cout << "Memory allocation failure!\n";
      cout << "Exception raised: " << str << '\n';
   }
}

I don't really se the difference and my is much more compact

compact and wrong. to make this do what you expect you'll have to use

Code:

buf = new(std::nothrow) char[512];

It doesn't help that the msdn example is out of date to the point of being wrong!
As hinted at, 'new' never returns NULL any more; it just throws.