C++中new失败时是抛出异常还是返回空指针

new

std::bad_alloc

new (std::nothrow)

nullptr

new

std::bad_alloc

new (std::nothrow)

nullptr

malloc

std::bad_alloc

new

nullptr

new

new

catch

new (std::nothrow)

new (std::nothrow)

nullptr

nullptr

new (std::nothrow)

new (std::nothrow)

malloc

new (std::nothrow)

nullptr

std::bad_alloc

main

try-catch

std::bad_alloc

new

try-catch

#include <iostream>
#include <vector>
#include <new> // For std::bad_alloc

void allocate_large_data() {
    // 尝试分配大量内存
    std::vector<int>* large_vec = nullptr;
    try {
        large_vec = new std::vector<int>(1024 * 1024 * 1024 / sizeof(int)); // 1GB
        std::cout << "Successfully allocated large vector." << std::endl;
        // ... 使用 large_vec ...
        delete large_vec;
    } catch (const std::bad_alloc& e) {
        std::cerr << "Caught std::bad_alloc in allocate_large_data: " << e.what() << std::endl;
        // 这里可以进行一些局部清理或日志记录
        if (large_vec) { // 确保即使分配失败，也处理可能的半构造对象（虽然bad_alloc通常在构造前）
            delete large_vec;
        }
        throw; // 重新抛出，让上层处理
    }
}

int main() {
    try {
        allocate_large_data();
    } catch (const std::bad_alloc& e) {
        std::cerr << "Global handler: Failed to allocate memory: " << e.what() << std::endl;
        // 在这里进行全局的错误处理，例如记录日志，向用户显示错误消息，然后退出
        return 1;
    } catch (const std::exception& e) {
        std::cerr << "Global handler: An unexpected error occurred: " << e.what() << std::endl;
        return 1;
    }
    return 0;
}

new (std::nothrow)

#include <iostream>
#include <memory> // For std::unique_ptr

int* create_int_array(size_t size) {
    int* arr = new (std::nothrow) int[size];
    if (arr == nullptr) {
        std::cerr << "Failed to allocate " << size << " integers. Returning nullptr." << std::endl;
        // 可以返回一个错误码，或者抛出一个自定义异常（如果需要）
    }
    return arr;
}

int main() {
    size_t large_size = 1024 * 1024 * 1024 / sizeof(int); // 1GB
    std::unique_ptr<int[]> my_array(create_int_array(large_size)); // 使用智能指针管理

    if (my_array) {
        std::cout << "Successfully allocated array with nothrow." << std::endl;
        // ... 使用 my_array ...
    } else {
        std::cout << "Array allocation failed with nothrow. Program can continue." << std::endl;
        // 可以尝试其他策略，比如使用更小的数组，或者从磁盘加载数据
    }

    size_t small_size = 10;
    std::unique_ptr<int[]> small_array(create_int_array(small_size));
    if (small_array) {
        std::cout << "Successfully allocated small array." << std::endl;
    }

    return 0;
}

std::unique_ptr

std::shared_ptr

new