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 |
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| allocation functions (function) |
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| allocates uninitialized storage (public member function of std::allocator) |
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[static] | allocates uninitialized storage using the allocator (public static member function of std::allocator_traits) |
| allocates memory (public member function of std::pmr::memory_resource) |
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| Allocate memory (public member function of std::pmr::polymorphic_allocator) |
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| allocates uninitialized storage using the outer allocator (public member function of std::scoped_allocator_adaptor) |
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Emptiness-checking functions |
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(C++17) | checks whether the container is empty (function) |
| checks whether the node handle is empty (public member function of node handle) |
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| checks whether the container is empty (public member function of std::array) |
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| checks whether the string is empty (public member function of std::basic_string) |
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| checks whether the view is empty (public member function of std::basic_string_view) |
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| checks whether the container is empty (public member function of std::deque) |
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| checks whether the container is empty (public member function of std::forward_list) |
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| checks whether the container is empty (public member function of std::list) |
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| checks whether the container is empty (public member function of std::map) |
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| checks whether the match was successful (public member function of std::match_results) |
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| checks whether the container is empty (public member function of std::multimap) |
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| checks whether the container is empty (public member function of std::multiset) |
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| checks whether the underlying container is empty (public member function of std::priority_queue) |
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| checks whether the underlying container is empty (public member function of std::queue) |
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| checks whether the container is empty (public member function of std::set) |
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| checks whether the underlying container is empty (public member function of std::stack) |
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| checks whether the container is empty (public member function of std::unordered_map) |
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| checks whether the container is empty (public member function of std::unordered_multimap) |
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| checks whether the container is empty (public member function of std::unordered_multiset) |
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| checks whether the container is empty (public member function of std::unordered_set) |
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| checks whether the container is empty (public member function of std::vector) |
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| checks if the path is empty (public member function of std::filesystem::path) |
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Miscellaneous |
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(C++11) | runs a function asynchronously (potentially in a new thread) and returns a std::future that will hold the result (function template) |
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(C++17) | pointer optimization barrier (function template) |
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