std::nothrow

 

C++

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工具庫

語言支持 庫功能特性測試宏 (C++20) 類型支持（基本類型、RTTI） 程序工具 可變參數函數 is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) 協程支持 (C++20) 契約支持 (C++26) 三路比較 three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

通用工具 函數對象 位操縱 (C++20) bitset hash (C++11) 關係運算符 (C++20 棄用) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= 整數比較函數 cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) 交換與類型運算 swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) 常用詞彙類型 pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23)

 

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voidify (僅用於闡述*) 分配器 allocator allocator_traits (C++11) allocation_result (C++23) scoped_allocator_adaptor (C++11) pmr::polymorphic_allocator (C++17) allocator_arg (C++11) uses_allocator (C++11) uses_allocator_construction_args (C++20) make_obj_using_allocator (C++20) uninitialized_construct_using_allocator (C++20) 未初始化內存算法 uninitialized_copy uninitialized_fill uninitialized_move (C++17) uninitialized_copy_n (C++11) uninitialized_fill_n uninitialized_move_n (C++17) construct_at (C++20) uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) destroy_n (C++17) destroy_at (C++17) 受約束的未初始化內存算法 ranges::uninitialized_copy (C++20) ranges::uninitialized_fill (C++20) ranges::uninitialized_move (C++20) ranges::uninitialized_copy_n (C++20)   ranges::uninitialized_fill_n (C++20) ranges::uninitialized_move_n (C++20) ranges::construct_at (C++20) ranges::uninitialized_default_construct (C++20) ranges::uninitialized_value_construct (C++20) ranges::destroy (C++20) ranges::uninitialized_default_construct_n (C++20)   ranges::uninitialized_value_construct_n (C++20) ranges::destroy_n (C++20) ranges::destroy_at (C++20) 內存資源 pmr::memory_resource (C++17) pmr::get_default_resource (C++17) pmr::set_default_resource (C++17) pmr::new_delete_resource (C++17) pmr::pool_options (C++17) pmr::null_memory_resource (C++17) pmr::synchronized_pool_resource (C++17) pmr::unsynchronized_pool_resource (C++17) pmr::monotonic_buffer_resource (C++17) 顯式生存期管理 start_lifetime_as (C++23) start_lifetime_as_array (C++23) 用於複合類設計的類型 indirect (C++26) polymorphic (C++26) 未初始化存儲 (C++20 前) raw_storage_iterator (C++17 棄用) get_temporary_buffer (C++17 棄用) return_temporary_buffer (C++17 棄用) 垃圾收集器支持 (C++23 前) declare_reachable (C++11)(C++23 前) declare_no_pointers (C++11)(C++23 前) pointer_safety (C++11)(C++23 前) undeclare_reachable (C++11)(C++23 前) undeclare_no_pointers (C++11)(C++23 前) get_pointer_safety (C++11)(C++23 前)

低層內存管理 operator newoperator new[] operator deleteoperator delete[] nothrow      nothrow_t new_handler set_new_handler get_new_handler (C++11) bad_alloc bad_array_new_length (C++11) align_val_t (C++17) destroying_delete_t (C++20) launder (C++17) 智能指針 unique_ptr (C++11) shared_ptr (C++11) weak_ptr (C++11) auto_ptr (C++17 前*) owner_less (C++11) owner_less<void> (C++17) owner_hash (C++26) owner_equal (C++26) enable_shared_from_this (C++11) bad_weak_ptr (C++11) default_delete (C++11) out_ptr_t (C++23) inout_ptr_t (C++23) 雜項 pointer_traits (C++11) to_address (C++20) addressof (C++11) align (C++11) assume_aligned (C++20) is_sufficiently_aligned (C++26) C 庫 malloc      free calloc realloc aligned_alloc (C++17) free_sized (C++26) free_aligned_sized (C++26) memalignment (C++26)

 

低層內存管理

函數

operator newoperator new[]

operator deleteoperator delete[]

get_new_handler (C++11)

set_new_handler

類

bad_alloc

bad_array_new_length (C++11)

align_val_t (C++17)

類型

new_handler

對象

nothrow

destroying_delete (C++20)

對象訪問

launder (C++17)

 

在標頭 <new> 定義
struct nothrow_t {};	(1)	(C++11 前)
struct nothrow_t { explicit nothrow_t() = default; };			(C++11 起)
extern const std::nothrow_t nothrow;	(2)

std::nothrow_t 一個空類類型，用於區分拋出與不拋出分配函數的重載。std::nothrow 是它的一個常量。

示例

運行此代碼

#include <iostream>
#include <new>

int main()
{
    try
    {
        while (true)
        {
            new int[100000000ul];   // 抛出重载
        }
    }
    catch (const std::bad_alloc& e)
    {
        std::cout << e.what() << '\n';
    }

    while (true)
    {
        int* p = new(std::nothrow) int[100000000ul]; // 不抛出重载
        if (p == nullptr)
        {
            std::cout << "分配返回了 nullptr\n";
            break;
        }
    }
}

輸出：

std::bad_alloc
分配返回了 nullptr

缺陷報告

下列更改行為的缺陷報告追溯地應用於以前出版的 C++ 標準。

缺陷報告	應用於	出版時的行為	正確行為
LWG 2510	C++11	默認構造函數非顯式，可能導致歧義	讓它顯式

參閱

operator newoperator new[]

分配函數 (函數)