If a function declared nodiscard or a function returning an enumeration or class declared nodiscard by value is called from a discarded-value expression other than a cast to void, the compiler is encouraged to issue a warning.
[[nodiscard]] |
Appears in a function declaration, enumeration declaration, or class declaration.
If a function declared nodiscard or a function returning an enumeration or class declared nodiscard by value is called from a discarded-value expression other than a cast to void, the compiler is encouraged to issue a warning.
struct [[nodiscard]] error_info { };
error_info enable_missile_safety_mode();
void launch_missiles();
void test_missiles() {
enable_missile_safety_mode(); // compiler may warn on discarding a nodiscard value
launch_missiles();
}
error_info& foo();
void f1() {
foo(); // nodiscard type is not returned by value, no warning
}The following standard functions are declared with nodiscard attribute:
Allocation functions |
|
| allocation functions (function) |
|
| allocates uninitialized storage (public member function of std::allocator<T>) |
|
|
[static] | allocates uninitialized storage using the allocator (public static member function of std::allocator_traits<Alloc>) |
| allocates memory (public member function of std::pmr::memory_resource) |
|
| Allocate memory (public member function of std::pmr::polymorphic_allocator<T>) |
|
| allocates uninitialized storage using the outer allocator (public member function of std::scoped_allocator_adaptor<OuterAlloc,InnerAlloc...>) |
|
Indirect access |
|
|
(C++17) | pointer optimization barrier (function template) |
|
(C++20) | informs the compiler that a pointer is aligned (function template) |
Emptiness-checking functions |
|
|
(C++17) | checks whether the container is empty (function template) |
| checks whether the node handle is empty (public member function of node handle) |
|
| checks whether the container is empty (public member function of std::array<T,N>) |
|
| checks whether the string is empty (public member function of std::basic_string<CharT,Traits,Allocator>) |
|
| checks whether the view is empty (public member function of std::basic_string_view<CharT,Traits>) |
|
| checks whether the container is empty (public member function of std::deque<T,Allocator>) |
|
| checks whether the container is empty (public member function of std::forward_list<T,Allocator>) |
|
| checks whether the container is empty (public member function of std::list<T,Allocator>) |
|
| checks whether the container is empty (public member function of std::map<Key,T,Compare,Allocator>) |
|
| checks whether the match was successful (public member function of std::match_results<BidirIt,Alloc>) |
|
| checks whether the container is empty (public member function of std::multimap<Key,T,Compare,Allocator>) |
|
| checks whether the container is empty (public member function of std::multiset<Key,Compare,Allocator>) |
|
| checks whether the underlying container is empty (public member function of std::priority_queue<T,Container,Compare>) |
|
| checks whether the underlying container is empty (public member function of std::queue<T,Container>) |
|
| checks whether the container is empty (public member function of std::set<Key,Compare,Allocator>) |
|
| checks if the sequence is empty (public member function of std::span<T,Extent>) |
|
| checks whether the underlying container is empty (public member function of std::stack<T,Container>) |
|
| checks whether the container is empty (public member function of std::unordered_map<Key,T,Hash,KeyEqual,Allocator>) |
|
| checks whether the container is empty (public member function of std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>) |
|
| checks whether the container is empty (public member function of std::unordered_multiset<Key,Hash,KeyEqual,Allocator>) |
|
| checks whether the container is empty (public member function of std::unordered_set<Key,Hash,KeyEqual,Allocator>) |
|
| checks whether the container is empty (public member function of std::vector<T,Allocator>) |
|
| checks if the path is empty (public member function of std::filesystem::path) |
|
Miscellaneous |
|
|
(C++11) | runs a function asynchronously (potentially in a new thread) and returns a std::future that will hold the result (function template) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/cpp/language/attributes/nodiscard