try\catch block in the main() function without brackets

Question

Visual Studio 2015; C++ language.

I remember that I read somewhere about the entry point (i.e. main method) what it is possible to write this:

#include <iostream>
using namespace std;

int main()
try{
  return 0; // I am here...
}
catch (...){
  cout << "I am 'catch'..." << endl; // This row wasn't called!
  return 1; // Oops... But the next `F10` key pressing jumps from the "try" 
  // block into this row!
}

I.e. at this case the try\catch block is located not in the brackets:

int main() { // start bracket
  try{
    return 0;
  }
  catch (...){
    return 1;
  }
} // end bracket

Both cases are compiled successfully and work too, but... In the first variant, when I am step by step pressing the F10 key after the try block I get into the catch block also. For the second variant of code I haven't such behaviour.

Why does it happen?

Answer 1

Your construction is a function-try-block and is defined in drafs n4296 for C++ 11 specification at 8.4 Function definitions [dcl.fct.def.general] with:

Function definitions have the form

• function-definition:
  • attribute-specifier-seq_opt decl-specifier-seq_opt declarator virt-specifier-seq_opt function-body
• function-body:
  • ctor-initializer_opt compound-statement
  • function-try-block
  • = default ;
  • = delete ;

and later in 15 Exception handling [except] with:

function-try-block:

• try ctor-initializer_opt compound-statement handler-seq

Examples suggest that the normal usage for a function-try-block should be a ctor, but it is valid for a normal function (and main is syntactically a mere function)

It is valid and works normally, meaning that catch block is only evaluated if an exception occurs in the ctor-initializer_opt on in the compound-statement. You can confirm it in your code by adding prints in your blocks or by testing return value.

In a Unix like system

foo
echo $?

should echo 0

In a Windows system under a CMD.exe windows

foo.exe
if errorlevel 1 echo "Catch block"

should not output Catch block

If your debugger lets you execute instructions in the catch block... it is not C++ 11 conformant!

But it is known that when exiting a block, MSVC debugger puts cursor on last line of block, I assume that is is what is happening here because the last line of the function-try-block is last line of catch.