蓝桥ROS机器人之现代C++学习笔记 第 5 章 智能指针与内存管理
【摘要】
为何一定要学习现代C++，因为在ROS中应用非常广，不学基础程序都看不懂的。
举例说明：
其实描述并不准确的，ROS1/2中使用的指针包括：
std::shared_ptrstd::unique_ptrstd::weak_ptr
例如：
virtual void publish(std...
为何一定要学习现代C++，因为在ROS中应用非常广，不学基础程序都看不懂的。
举例说明：
其实描述并不准确的，ROS1/2中使用的指针包括：
- std::shared_ptr
- std::unique_ptr
- std::weak_ptr
例如：
-
virtual void
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publish(std::unique_ptr<MessageT, MessageDeleter> & msg)
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{
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this->do_inter_process_publish(msg.get());
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if (store_intra_process_message_) {
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// Take the pointer from the unique_msg, release it and pass as a void *
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// to the ipm. The ipm should then capture it again as a unique_ptr of
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// the correct type.
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// TODO(wjwwood):
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// investigate how to transfer the custom deleter (if there is one)
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// from the incoming unique_ptr through to the ipm's unique_ptr.
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// See: http://stackoverflow.com/questions/11002641/dynamic-casting-for-unique-ptr
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MessageT * msg_ptr = msg.get();
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msg.release();
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uint64_t message_seq =
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store_intra_process_message_(intra_process_publisher_id_, msg_ptr, typeid(MessageT));
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rcl_interfaces::msg::IntraProcessMessage ipm;
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ipm.publisher_id = intra_process_publisher_id_;
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ipm.message_sequence = message_seq;
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auto status = rcl_publish(&intra_process_publisher_handle_, &ipm);
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if (RCL_RET_PUBLISHER_INVALID == status) {
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rcl_reset_error(); // next call will reset error message if not context
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if (rcl_publisher_is_valid_except_context(&intra_process_publisher_handle_)) {
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rcl_context_t * context = rcl_publisher_get_context(&intra_process_publisher_handle_);
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if (nullptr != context && !rcl_context_is_valid(context)) {
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// publisher is invalid due to context being shutdown
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return;
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}
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}
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}
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if (RCL_RET_OK != status) {
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rclcpp::exceptions::throw_from_rcl_error(status, "failed to publish intra process message");
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}
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} else {
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// Always destroy the message, even if we don't consume it, for consistency.
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msg.reset();
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}
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}
以及：
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#include <memory>
-
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void unique_func_ref(std::unique_ptr<int> & msg) {}
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void unique_func_value(std::unique_ptr<int> msg) {}
-
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int main(int argc, char ** argv)
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{
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std::unique_ptr<int> foo(new int);
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std::unique_ptr<int> bar(new int);
-
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unique_func_ref(foo);
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// does not compile
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// unique_func_value(bar);
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unique_func_value(std::move(bar));
-
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return 0;
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}
不学习现代C++，ROS1/2机器人编程连门都入不了啊………………
我自己从写C++的第一个hello world，到今天已经24年过去了，但还是水平菜如小白。
只能继续努力学习了。
智能指针C++11就已经引入了，让程序员不再需要关心手动释放内存。
（克服了传统C++，使用
new和delete去 『手工操作（不能忘会内存泄漏的？）』对资源进行释放。）
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#include <iostream>
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#include <memory>
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void foo(std::shared_ptr<int> i)
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{
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(*i)++;
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}
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int main()
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{
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// auto pointer = new int(10); // illegal, no direct assignment
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// std::shared_ptr construction
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auto pointer = std::make_shared<int>(10);
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auto pointer2 = pointer; // reference count + 1
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auto pointer3 = pointer; // reference count + 1
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-
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foo(pointer);
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std::cout << *pointer << std::endl; // 11
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int *p = pointer.get(); // does not increase reference count
-
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std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
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std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
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std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
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pointer2.reset();
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std::cout << "reset pointer2:" << std::endl;
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std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
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std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
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std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
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pointer3.reset();
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std::cout << "reset pointer3:" << std::endl;
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std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
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std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
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std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
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// std::cout << *pointer << std::endl; // reference count equals 0, illegal access
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-
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// Before leaving the scope, the pointer is destructed and
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// the reference count is reduced to 0
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return 0;
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}
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#include <iostream>
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#include <memory>
-
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struct Foo {
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Foo() { std::cout << "Foo::Foo" << std::endl; }
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~Foo() { std::cout << "Foo::~Foo" << std::endl; }
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void foo() { std::cout << "Foo::foo" << std::endl; }
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};
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void f(const Foo &) {
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std::cout << "f(const Foo&)" << std::endl;
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}
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int main() {
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std::unique_ptr<Foo> p1(std::make_unique<Foo>());
-
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// p1 is not empty, prints
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if (p1) p1->foo();
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{
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std::unique_ptr<Foo> p2(std::move(p1));
-
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// p2 is not empty, prints
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f(*p2);
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// p2 is not empty, prints
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if(p2) p2->foo();
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// p1 is empty, no prints
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if(p1) p1->foo();
-
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p1 = std::move(p2);
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// p2 is empty, no prints
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if(p2) p2->foo();
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std::cout << "p2 was destroyed" << std::endl;
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}
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// p1 is not empty, prints
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if (p1) p1->foo();
-
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// Foo instance will be destroyed when leaving the scope
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}
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#include <iostream>
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#include <memory>
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class A;
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class B;
-
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class A {
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public:
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std::shared_ptr<B> pointer;
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~A() {
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std::cout << "A was destroyed" << std::endl;
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}
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};
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class B {
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public:
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std::shared_ptr<A> pointer;
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~B() {
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std::cout << "B was destroyed" << std::endl;
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}
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};
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int main() {
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std::shared_ptr<A> a = std::make_shared<A>();
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std::shared_ptr<B> b = std::make_shared<B>();
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a->pointer = b;
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b->pointer = a;
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return 0;
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}
文章来源: zhangrelay.blog.csdn.net，作者：zhangrelay，版权归原作者所有，如需转载，请联系作者。
原文链接：zhangrelay.blog.csdn.net/article/details/124067964
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