c++中的std::allocator是什么_自定义内存分配器机制与应用示例

#include <iostream>
#include <memory>
<p>int main() {
std::allocator<int> alloc;</p><pre class="brush:php;toolbar:false;"><pre class="brush:php;toolbar:false;">// 分配可容纳1个int的内存
int* p = alloc.allocate(1);

// 在p指向的内存构造int值为42
std::construct_at(p, 42);

std::cout << *p << "\n";  // 输出 42

// 析构对象
std::destroy_at(p);

// 释放内存
alloc.deallocate(p, 1);

return 0;

#include <iostream>
#include <vector>
#include <cstddef>
<p>template<typename T, size_t N = 1024>
class stack_allocator {
private:
alignas(T) char pool[N * sizeof(T)];
bool used[N] = {false};</p><p>public:
using value_type = T;</p><pre class="brush:php;toolbar:false;"><pre class="brush:php;toolbar:false;">stack_allocator() = default;
template<typename U>
stack_allocator(const stack_allocator<U, N>&) {}

T* allocate(size_t n) {
    if (n != 1 || n > N) 
        throw std::bad_alloc();

    for (size_t i = 0; i < N; ++i) {
        if (!used[i]) {
            used[i] = true;
            return reinterpret_cast<T*>(pool + i * sizeof(T));
        }
    }
    throw std::bad_alloc();
}

void deallocate(T* p, size_t n) {
    if (p == nullptr) return;

    size_t index = (reinterpret_cast<char*>(p) - pool) / sizeof(T);
    if (index < N && used[index]) {
        used[index] = false;
    }
}

int main() {
    // 使用 stack_allocator 的 vector
    std::vector<int, stack_allocator<int, 100>> vec;
<pre class="brush:php;toolbar:false;"><pre class="brush:php;toolbar:false;">for (int i = 0; i < 10; ++i) {
    vec.push_back(i * 10);
}

for (int val : vec) {
    std::cout << val << " ";
}
std::cout << "\n";

return 0;