Scope Guard & Defer C++

  _____                         _____                     _    _____
 / ____|                       / ____|                   | |  / ____|_     _
| (___   ___ ___  _ __   ___  | |  __ _   _  __ _ _ __ __| | | |   _| |_ _| |_
 \___ \ / __/ _ \| '_ \ / _ \ | | |_ | | | |/ _` | '__/ _` | | |  |_   _|_   _|
 ____) | (_| (_) | |_) |  __/ | |__| | |_| | (_| | | | (_| | | |____|_|   |_|
|_____/ \___\___/| .__/ \___|  \_____|\__,_|\__,_|_|  \__,_|  \_____|
                 | |
                 |_|

Branch	Linux/OSX	Windows	License	Codacy
master

Scope Guard statement invokes a function with deferred execution until surrounding function returns in cases:

Surrounding function executed return statemeent
This function reached the end of its body
Erros occure

Program control transferring does not influence Scope Guard statement execution. Hence, Scope Guard statement can be used to perform manual resource management, such as file descriptors closing, and to perform actions even if an error occure.

Features

Simple syntax
C++11
Header-only
Dependency-free
Thin callback wrapping: no added std::function or virtual table penalties
No implicitly ignored return, check callback return void
Defer or Scope Guard syntax

Examples

Scope Guard syntax

std::fstream file("test.txt");
SCOPE_EXIT{ file.close(); }; // File closes when exit the enclosing scope or errors occure.

Custom Scope Guard

persons.push_back(person); // Add the person to db.
MAKE_SCOPE_EXIT(scope_exit){ // Following block is executed when exit the enclosing scope or errors occure.
  persons.pop_back(); // If the db insertion fails, we should roll back.
};
// ...
scope_exit.Dismiss(); // An exception was not thrown, so don't execute the scope_exit.

Defer syntax

std::fstream file("test.txt");
DEFER{ file.close(); }; // File closes when exit the enclosing scope or errors occure.

Custom Defer

persons.push_back(person); // Add the person to db.
MAKE_DEFER(defer){ // Following block is executed when exit the enclosing scope or errors occure.
  persons.pop_back(); // If the db insertion fails, we should roll back.
};
// ...
defer.Dismiss(); // An exception was not thrown, so don't execute the defer.

Remarks

If multiple Scope Guard statements appear in the same scope, the order they appear is the reverse of the order they are executed.

void f() {
  SCOPE_EXIT{ std::cout << "First" << std::endl; };
  SCOPE_EXIT{ std::cout << "Second" << std::endl; };
  SCOPE_EXIT{ std::cout << "Third" << std::endl; };
  ... // Other code.
  // Prints "Third".
  // Prints "Second".
  // Prints "First".
}

Integration

You should add required file scope_guard.hpp and switch to C++11

Compiler compatibility

GCC
Clang
MSVC

References

Andrei Alexandrescu "Systematic Error Handling in C++"

Andrei Alexandrescu “Declarative Control Flow"

nmarwen / scope_guard