noexcept operator (since C++11)

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

C++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (C++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function expression
inline specifier
Dynamic exception specifications (until C++17*)
noexcept specifier (C++11)
Exceptions
throw-expression try block	handler
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Class/struct types Union types
Specifiers
const/volatile decltype (C++11) auto (C++11)	constexpr (C++11) consteval (C++20) constinit (C++20)
Storage duration specifiers
Initialization
Default-initialization Value-initialization Zero-initialization Copy-initialization Direct-initialization	Aggregate initialization List-initialization (C++11)   Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (C++11)
User-defined (C++11)
Utilities
Attributes (C++11)
Types
typedef declaration
Type alias declaration (C++11)
Casts
Implicit conversions static_cast const_cast	Explicit conversions dynamic_cast reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Constructors this pointer	Access specifiers friend specifier
Class-specific function properties
Virtual function override specifier (C++11)   final specifier (C++11)	explicit (C++11) static
Special member functions
Default constructor Copy constructor Move constructor (C++11)	Copy assignment Move assignment (C++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (C++11)
Miscellaneous
Inline assembly	History of C++

 

Exceptions

try block

Throwing exceptions

Handling exceptions

Exception specification

noexcept specification (C++11)

dynamic specification (until C++17*)

noexcept operator (C++11)

 

The noexcept operator performs a compile-time check that returns true if an expression is declared to not throw any exceptions.

It can be used within a function template's noexcept specifier to declare that the function will throw exceptions for some types but not others.

Syntax

noexcept( expression )

Returns a prvalue of type bool.

Explanation

The noexcept operator does not evaluate expression. The result is false if the expression contains at least one of the following potentially evaluated constructs:

• call to any type of function that does not have non-throwing exception specification, unless it is a constant expression.
• throw expression.
• dynamic_cast expression when the target type is a reference type, and conversion needs a run time check
• typeid expression when argument type is polymorphic class type

In all other cases the result is true.

Keywords

noexcept

Example

Run this code

#include <iostream>
#include <utility>
 
void may_throw();
void no_throw() noexcept;
auto lmay_throw = []{};
auto lno_throw = []() noexcept {};
class T{
public:
  ~T(){}
};
int main()
{
 
 
  std::cout << std::boolalpha
            << "Is may_throw() noexcept? " << noexcept(may_throw()) << '\n'
            << "Is no_throw() noexcept? " << noexcept(no_throw()) << '\n'
            << "Is lmay_throw() noexcept? " << noexcept(lmay_throw()) << '\n'
            << "Is lno_throw() noexcept? " << noexcept(lno_throw()) << '\n'
            << "Is ~T() noexcept? " << noexcept(std::declval<T>().~T()) << '\n';
 
 
 
 
}

See also

noexcept specifier(C++11)	specifies whether a function could throw exceptions
Dynamic exception specification(until C++17)	specifies what exceptions are thrown by a function (deprecated in C++11)