Can NULL be used in consortium in C language?
Apr 03, 2025 am 10:36 AM
In C, NULL can be used in a union, but needs to be handled with caution. Because NULL can cause undefined behavior at different members in the union, it is best to define a clear invalid value for each member as needed.
Can NULL be used in a union in C? The answer is: Yes, but be cautious!
This question seems simple, but it actually has a secret. On the surface, NULL is a null pointer, and a consortium is a guy who can store different types of data. It seems no big deal to stuff the empty pointer into the consortium. But in fact, this involves data types, memory alignment, and potential undefined behaviors, and you will fall into the pit if you are not careful.
Let's review the basics first. NULL is usually defined as (void *)0 in C language, representing a null pointer to an empty address. As for the union, all its members share the same memory space, and only one member is valid at the same time. The key is that different types of members may occupy different memory sizes, and the compiler will perform memory alignment in order to optimize performance.
Now, suppose we have a consortium:
<code class="c">union MyUnion { int i; char *ptr; };</code>
We can use this:
<code class="c">union MyUnion u; u.ptr = NULL;</code>
There are no syntax errors in this code, and the compiler will accept it happily. NULL was successfully assigned to ptr members. But the question is, what happens when you subsequently access ui ? The result is undefined! Because NULL (usually 0) is interpreted as an integer, which may differ from the default value of type int , or may conflict with the actual representation of int in memory. The result you get may be 0, or other random values, and may even cause the program to crash.
Let's take a look at a more complex example:
<code class="c">union MyUnion { long long ll; char *ptr; double d; }; int main() { union MyUnion u; u.ptr = NULL; printf("Size of union: %zu\n", sizeof(u)); printf("u.ll: %lld\n", u.ll); // 潛在的危險(xiǎn)！ return 0; }</code>
In this example, the union contains three different size members: long long , char * and double . The result of sizeof(u) depends on how the compiler aligns these members. Accessing u.ll is also dangerous, because NULL may cause inconsistency in long long memory layout, resulting in wrong values ??being read.
So, while syntactically allowing, putting NULL into a union is usually not a good idea. It increases the complexity and unpredictability of the code. It is better to define a clear "invalid" value for each member of the union as needed. For example, for pointer members, a special pointer value can be defined (for example, a pointer to a known invalid address, but be careful to avoid accessing this address), and for numeric members, a special value (for example -1 or a large number) can be used to represent the invalid state. This is safer, clearer, and easier to debug than using NULL directly.
All in all, although C allows you to put NULL into a union, this is an error-prone practice and it is recommended to avoid it as much as possible. It is king to clearly define invalid states and write more robust code. Remember, the robustness of a program is much more important than the simplicity of the code.
The above is the detailed content of Can NULL be used in consortium in C language?. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
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
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
The popularity of the currency circle has returned, why do smart people have begun to quietly increase their positions? Look at the trend from the on-chain data and grasp the next round of wealth password!
Jul 09, 2025 pm 08:30 PM
As the market conditions pick up, more and more smart investors have begun to quietly increase their positions in the currency circle. Many people are wondering what makes them take decisively when most people wait and see? This article will analyze current trends through on-chain data to help readers understand the logic of smart funds, so as to better grasp the next round of potential wealth growth opportunities.
What are the mainstream public chains of cryptocurrencies? The top ten rankings of cryptocurrency mainstream public chains in 2025
Jul 10, 2025 pm 08:21 PM
The pattern in the public chain field shows a trend of "one super, many strong ones, and a hundred flowers blooming". Ethereum is still leading with its ecological moat, while Solana, Avalanche and others are challenging performance. Meanwhile, Polkadot, Cosmos, which focuses on interoperability, and Chainlink, which is a critical infrastructure, form a future picture of multiple chains coexisting. For users and developers, choosing which platform is no longer a single choice, but requires a trade-off between performance, cost, security and ecological maturity based on specific needs.
Cardano's smart contract evolution: The impact of Alonzo upgrades on 2025
Jul 10, 2025 pm 07:36 PM
Cardano's Alonzo hard fork upgrade has successfully transformed Cardano from a value transfer network to a fully functional smart contract platform by introducing the Plutus smart contract platform. 1. Plutus is based on Haskell language, with powerful functionality, enhanced security and predictable cost model; 2. After the upgrade, dApps deployment is accelerated, the developer community is expanded, and the DeFi and NFT ecosystems are developing rapidly; 3. Looking ahead to 2025, the Cardano ecosystem will be more mature and diverse. Combined with the improvement of scalability in the Basho era, the enhancement of cross-chain interoperability, the evolution of decentralized governance in the Voltaire era, and the promotion of mainstream adoption by enterprise-level applications, Cardano has
Bitcoin breaks new highs, Dogecoin rebounds strongly, will Ethereum keep up with the pace
Jul 09, 2025 pm 08:24 PM
Recently, Bitcoin hit a new high, Dogecoin ushered in a strong rebound and the market was hot. Next, we will analyze the market drivers and technical aspects to determine whether Ethereum still has opportunities to follow the rise.
The top 5 most worth investing in 2025 (with latest data)
Jul 09, 2025 am 06:06 AM
The five most valuable stablecoins in 2025 are Tether (USDT), USD Coin (USDC), Dai (DAI), First Digital USD (FDUSD) and TrueUSD (TUSD).
Who issues stablecoins? What are the stablecoins?
Jul 09, 2025 pm 06:24 PM
Stablecoins are crypto assets that maintain price stability by anchoring fiat currencies such as the US dollar. They are mainly divided into three categories: fiat currency collateral, crypto asset collateral and algorithmic stablecoins. 1. USDT is issued by Tether and is the stablecoin with the largest market value and the highest liquidity. 2. USDC is released by the Centre alliance launched by Circle and Coinbase, and is known for its transparency and compliance. 3. DAI is generated by MakerDAO through over-collateralization of crypto assets and is the core currency in the DeFi field. 4. BUSD was launched in partnership with Paxos, and is regulated by the United States but has been discontinued. 5. TUSD achieves high transparency reserve verification through third-party escrow accounts. Users can use centralized exchanges such as Binance, Ouyi, and Huobi
The flow of funds on the chain is exposed: What new tokens are being bet on by Clever Money?
Jul 16, 2025 am 10:15 AM
Ordinary investors can discover potential tokens by tracking "smart money", which are high-profit addresses, and paying attention to their trends can provide leading indicators. 1. Use tools such as Nansen and Arkham Intelligence to analyze the data on the chain to view the buying and holdings of smart money; 2. Use Dune Analytics to obtain community-created dashboards to monitor the flow of funds; 3. Follow platforms such as Lookonchain to obtain real-time intelligence. Recently, Cangming Money is planning to re-polize LRT track, DePIN project, modular ecosystem and RWA protocol. For example, a certain LRT protocol has obtained a large amount of early deposits, a certain DePIN project has been accumulated continuously, a certain game public chain has been supported by the industry treasury, and a certain RWA protocol has attracted institutions to enter.
Which chain does Dogecoin DOGE belong to? Does Dogecoin belong to the Binance Chain?
Jul 10, 2025 pm 08:39 PM
Recently, the discussion in the digital asset field has remained hot. Dogecoin DOGE, as one of the most popular focus, has become a question that many people have explored. Where does it "settling down"? What is the relationship with the current leading trading platform, Binance? To answer these questions, we need to conduct in-depth analysis from the two dimensions of the underlying technical logic of digital assets and the platform ecology, rather than just staying in appearance.
