5

Function try-catch blocks

 3 years ago
source link: https://vorbrodt.blog/2019/04/02/function-try-catch-blocks/
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
neoserver,ios ssh client

Function try-catch blocks

Syntactic sugar or a useful feature? More than just sweet sweet sugar baby! This little known feature is a nice way of wrapping an entire function in a try catch block. So instead of writing this:

void eat_it()
throw runtime_error("System error from eat_it()");
catch(exception& e)
cout << "Swallowing: " << e.what() << endl;

You can write this:

void eat_it_sugar() try
throw runtime_error("System error from eat_it_sugar()");
catch(exception& e)
cout << "Swallowing: " << e.what() << endl;

The meaning of the two functions is identical. Notice here I’m swallowing the exception instead of propagating it out. I could call throw to re-throw it, or in both cases I could throw a different exception inside the catch block.

The caveat is with function try-catch blocks around constructors: they have to re-throw the same or different exception. If you don’t re-throw explicitly the compiler will do it for you. It is also useful for catching exceptions emitted during the initialization of member variables, and throwing something else (or re-throwing the same). Like this:

struct P
P() { throw logic_error("Logic error from P::P()"); }
struct Q
Q() try : m_P()
cout << "Never printed!" << endl;
catch(exception& e)
cout << "Inside Q::Q() caught: " << e.what() << endl;
throw runtime_error("Runtime error from Q::Q()");
P m_P;

Complete listing (try_block.cpp):

#include <iostream>
#include <stdexcept>
using namespace std;
struct P
P() { throw logic_error("Logic error from P::P()"); }
struct Q
Q() try : m_P()
cout << "Never printed!" << endl;
catch(exception& e)
cout << "Inside Q::Q() caught: " << e.what() << endl;
throw runtime_error("Runtime error from Q::Q()");
P m_P;
void eat_it()
throw runtime_error("System error from eat_it()");
catch(exception& e)
cout << "Swallowing: " << e.what() << endl;
void eat_it_sugar() try
throw runtime_error("System error from eat_it_sugar()");
catch(exception& e)
cout << "Swallowing: " << e.what() << endl;
int main() try
eat_it();
eat_it_sugar();
catch(exception& e)
cout << "Inside main() caught: " << e.what() << endl;

Swallowing: System error from eat_it()
Swallowing: System error from eat_it_sugar()
Inside Q::Q() caught: Logic error from P::P()
Inside main() caught: Runtime error from Q::Q()

Program output.


report

Recommend

About Joyk


Aggregate valuable and interesting links.
Joyk means Joy of geeK