Backend DevelopmentC++What are the Valid States of Moved-from Objects in C 11 and How to Define Them?What are the Valid States of Moved-from Objects in C 11 and How to Define Them?
Understanding Valid States for Moved-from Objects in C 11
Move semantics in C 11 introduce a crucial concept: the state of objects after being moved from. However, the exact conditions that a moved-from object must satisfy can be confusing.
The Issue with pimpl Objects
Consider the pimpl idiom, where a class wraps a pointer to an implementation object. If we move from a Foo object (containing a std::unique_ptr
- Destroying or assigning to it is safe.
- Calling member functions (via the implementation pointer) is problematic, as it may reference a deleted object.
Standard Library Moved-from States
The C standard defines that moved-from objects of standard library types are placed in an "unspecified but valid state." This means that you can perform operations on them that have valid preconditions.
However, for non-standard types, you must define and document the valid state and operations allowed after being moved from.
Defining the Valid State for pimpl
In the Foo example, we could specify that moving from it renders the do_stuff function invalid. This would prevent us from accidentally invoking it on a moved-from object.
Avoiding Dynamic Allocations
To avoid the overhead of dynamic allocations when checking the valid state, consider using the "null object" pattern. This involves having a default FooImpl that is used when the object is in an invalid state.
Concepts and Moved-from Objects
Finally, note that moved-from objects must still meet the requirements of standard library concepts. If your type doesn't remain in a valid state, using it with standard library functions may result in undefined behavior.
The above is the detailed content of What are the Valid States of Moved-from Objects in C 11 and How to Define Them?. For more information, please follow other related articles on the PHP Chinese website!
C# and C : Exploring the Different ParadigmsMay 08, 2025 am 12:06 AMThe main differences between C# and C are memory management, polymorphism implementation and performance optimization. 1) C# uses a garbage collector to automatically manage memory, while C needs to be managed manually. 2) C# realizes polymorphism through interfaces and virtual methods, and C uses virtual functions and pure virtual functions. 3) The performance optimization of C# depends on structure and parallel programming, while C is implemented through inline functions and multithreading.
C XML Parsing: Techniques and Best PracticesMay 07, 2025 am 12:06 AMThe DOM and SAX methods can be used to parse XML data in C. 1) DOM parsing loads XML into memory, suitable for small files, but may take up a lot of memory. 2) SAX parsing is event-driven and is suitable for large files, but cannot be accessed randomly. Choosing the right method and optimizing the code can improve efficiency.
C in Specific Domains: Exploring Its StrongholdsMay 06, 2025 am 12:08 AMC is widely used in the fields of game development, embedded systems, financial transactions and scientific computing, due to its high performance and flexibility. 1) In game development, C is used for efficient graphics rendering and real-time computing. 2) In embedded systems, C's memory management and hardware control capabilities make it the first choice. 3) In the field of financial transactions, C's high performance meets the needs of real-time computing. 4) In scientific computing, C's efficient algorithm implementation and data processing capabilities are fully reflected.
Debunking the Myths: Is C Really a Dead Language?May 05, 2025 am 12:11 AMC is not dead, but has flourished in many key areas: 1) game development, 2) system programming, 3) high-performance computing, 4) browsers and network applications, C is still the mainstream choice, showing its strong vitality and application scenarios.
C# vs. C : A Comparative Analysis of Programming LanguagesMay 04, 2025 am 12:03 AMThe main differences between C# and C are syntax, memory management and performance: 1) C# syntax is modern, supports lambda and LINQ, and C retains C features and supports templates. 2) C# automatically manages memory, C needs to be managed manually. 3) C performance is better than C#, but C# performance is also being optimized.
Building XML Applications with C : Practical ExamplesMay 03, 2025 am 12:16 AMYou can use the TinyXML, Pugixml, or libxml2 libraries to process XML data in C. 1) Parse XML files: Use DOM or SAX methods, DOM is suitable for small files, and SAX is suitable for large files. 2) Generate XML file: convert the data structure into XML format and write to the file. Through these steps, XML data can be effectively managed and manipulated.
XML in C : Handling Complex Data StructuresMay 02, 2025 am 12:04 AMWorking with XML data structures in C can use the TinyXML or pugixml library. 1) Use the pugixml library to parse and generate XML files. 2) Handle complex nested XML elements, such as book information. 3) Optimize XML processing code, and it is recommended to use efficient libraries and streaming parsing. Through these steps, XML data can be processed efficiently.
C and Performance: Where It Still DominatesMay 01, 2025 am 12:14 AMC still dominates performance optimization because its low-level memory management and efficient execution capabilities make it indispensable in game development, financial transaction systems and embedded systems. Specifically, it is manifested as: 1) In game development, C's low-level memory management and efficient execution capabilities make it the preferred language for game engine development; 2) In financial transaction systems, C's performance advantages ensure extremely low latency and high throughput; 3) In embedded systems, C's low-level memory management and efficient execution capabilities make it very popular in resource-constrained environments.
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),
EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function
SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.
SublimeText3 English version
Recommended: Win version, supports code prompts!
PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool
