C++智能指针定制删除器

C++智能指针定制删除器

智能指针的自定义删除器扩展了智能指针的功能，使其不仅可以管理内存，还能管理文件句柄、套接字、数据库连接等资源。

unique_ptr支持自定义删除器作为模板参数。

#include
#include
#include

struct FileDeleter {
void operator()(FILE* fp) const {
if (fp) {
std::fclose(fp);
std::cout << "File closed by custom deleter\n";
}
}
};

struct SocketDeleter {
void operator()(int* sock) const {
if (sock) {
#ifdef _WIN32
closesocket(*sock);
#else
close(*sock);
#endif
std::cout << "Socket closed\n";
delete sock;
}
}
};

void file_deleter_example() {
std::unique_ptr file(std::fopen("test.txt", "w"));
if (file) {
std::fprintf(file.get(), "Custom deleter example\n");
}
std::cout << "File will be automatically closed\n";
}

lambda自定义删除器。

void lambda_deleter() {
auto file_deleter = [](FILE* fp) {
if (fp) {
std::fclose(fp);
std::cout << "File closed by lambda deleter\n";
}
};

std::unique_ptr file(
std::fopen("lambda.txt", "w"), file_deleter);

if (file) {
std::fprintf(file.get(), "Lambda deleter example\n");
}
}

shared_ptr也支持自定义删除器。

void shared_ptr_deleter() {
auto deleter = [](int* p) {
std::cout << "Custom shared_ptr deleter\n";
delete p;
};

std::shared_ptr ptr(new int(42), deleter);
std::cout << "Value: " << *ptr << "\n";
}

shared_ptr的删除器类型擦除。

void type_erased_deleter() {
auto file = std::shared_ptr(std::fopen("shared.txt", "w"),
[](FILE* fp) {
if (fp) {
std::fclose(fp);
std::cout << "File closed via shared_ptr\n";
}
});

if (file) {
std::fprintf(file.get(), "Shared pointer file\n");
}
}

自定义删除器管理SQLite连接。

struct SQLiteDeleter {
void operator()(void* db) const {
if (db) {
std::cout << "SQLite database closed\n";
}
}
};

void sqlite_example() {
// std::unique_ptr db(sqlite3_open(":memory:"));
std::cout << "Database connection managed by smart pointer\n";
}

自定义删除器管理POSIX定时器。

struct TimerDeleter {
void operator()(timer_t* timer) const {
if (timer) {
timer_delete(*timer);
delete timer;
std::cout << "Timer deleted\n";
}
}
};

void timer_example() {
std::unique_ptr timer(new timer_t);
std::cout << "POSIX timer managed\n";
}

自定义删除器管理mmap内存映射。

struct MMapDeleter {
size_t length;
explicit MMapDeleter(size_t len) : length(len) {}

void operator()(void* ptr) const {
if (ptr && ptr != MAP_FAILED) {
munmap(ptr, length);
std::cout << "Memory unmapped\n";
}
}
};

void mmap_example() {
size_t size = 4096;
// void* ptr = mmap(nullptr, size, PROT_READ | PROT_WRITE,
// MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
// std::unique_ptr mem(ptr, MMapDeleter(size));
std::cout << "Memory mapping would be managed by smart pointer\n";
}

带状态的删除器。

class StatefulDeleter {
std::string context_;
public:
explicit StatefulDeleter(std::string ctx) : context_(std::move(ctx)) {}

void operator()(FILE* fp) const {
if (fp) {
std::fclose(fp);
std::cout << "Closed file [" << context_ << "]\n";
}
}
};

void stateful_deleter_example() {
StatefulDeleter deleter("important_data");
std::unique_ptr file(
std::fopen("stateful.txt", "w"), deleter);

if (file) {
std::fprintf(file.get(), "Stateful deleter\n");
}
}

自定义删除器在资源池中的应用。

class ResourcePool {
std::vector available_;
public:
struct PoolDeleter {
ResourcePool* pool;
explicit PoolDeleter(ResourcePool* p) : pool(p) {}

void operator()(int* ptr) const {
pool->release(ptr);
}
};

std::unique_ptr acquire() {
int* ptr;
if (available_.empty()) {
ptr = new int(0);
} else {
ptr = available_.back();
available_.pop_back();
}
return std::unique_ptr(ptr, PoolDeleter(this));
}

void release(int* ptr) {
available_.push_back(ptr);
std::cout << "Resource returned to pool\n";
}

~ResourcePool() {
for (auto* p : available_) delete p;
}
};

void pool_deleter_example() {
ResourcePool pool;
{
auto resource = pool.acquire();
*resource = 42;
std::cout << "Acquired: " << *resource << "\n";
}
}

自定义删除器使智能指针能管理任何需要释放的资源，是RAII的通用实现。