C++异常安全vector 内存分配失败处理

template<typename T>
void vector<T>::reserve(size_t new_cap) {
    if (new_cap <= capacity_) return;
<pre class="brush:php;toolbar:false;"><pre class="brush:php;toolbar:false;">T* new_data = static_cast<T*>(::operator new(new_cap * sizeof(T)));
try {
    for (size_t i = 0; i < size_; ++i) {
        new(&new_data[i]) T(data_[i]); // 复制构造
    }
} catch (...) {
    ::operator delete(new_data);
    throw; // 异常继续传播，但vector状态未变
}

// 仅当复制成功后才释放旧内存
for (size_t i = 0; i < size_; ++i) {
    data_[i].~T();
}
::operator delete(data_);

data_ = new_data;
capacity_ = new_cap;

std::allocator<T> alloc;
T* new_block = alloc.allocate(new_capacity);

void push_back(const T& value) {
    if (size_ == capacity_) {
        size_t new_cap = capacity_ ? capacity_ * 2 : 1;
        T* new_data = alloc_.allocate(new_cap);
<pre class="brush:php;toolbar:false;"><pre class="brush:php;toolbar:false;">    try {
        new(&new_data[size_]) T(value); // 先构造新元素
        for (size_t i = 0; i < size_; ++i) {
            new(&new_data[i]) T(std::move_if_noexcept(data_[i]));
        }
    } catch (...) {
        if (new_data[size_] 已构造)
            new_data[size_].~T();
        alloc_.deallocate(new_data, new_cap);
        throw;
    }

    // 成功后析构旧对象并释放
    for (size_t i = 0; i < size_; ++i) {
        data_[i].~T();
    }
    alloc_.deallocate(data_, capacity_);

    data_ = new_data;
    capacity_ = new_cap;
} else {
    new(&data_[size_]) T(value);
}
++size_;

void* ptr = ::operator new(size, std::nothrow);
if (!ptr) {
    // 处理分配失败：抛出自定义异常、记录日志、尝试释放缓存等
}