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Have you ever read the source code of the Linux kernel? During the process of<span>Linux</span> driver development, have you encountered such a warning?
WARNING: do not add new typedefs
Using<span>typedef</span> is not allowed!
Although it’s just a warning, if you want to submit code to the open-source repository, this is a must-optimize item.
So, why does the<span>Linux</span> kernel discourage the use of<span>typedef</span>?
1. Linus Torvalds’ Attitude
> On Mon, 10 Jun 2002, Linus Torvalds wrote:
>> –snip/snip
> > But in the end, maintainership matters. I personally don’t want the
> > typedef culture to get the upper hand, but I don’t mind a few of them, and
> > people who maintain their own code usually get the last word.
>> to sum it up:
>> using the “struct mystruct” is recommended, but not a must.
<span>Torvalds </span> himself does not want to see the<span>typedef</span> culture dominate, but those who maintain their own code usually have the final say.
<span>Torvalds </span>still recommends using the structure of<span>struct mystruct</span>.- Hard to Understand: Using
<span>typedef</span>types makes it difficult to understand what the actual type of the variable is. - Poor Maintainability: Due to the vast architecture of the
<span>Linux</span>kernel, the<span>typedef</span>types defined across different architectures may not be universally applicable.
<span>Torvalds </span> original text can be found at: https://lkml.indiana.edu/hypermail/linux/kernel/0206.1/0402.html
2. Kernel Coding Standards
From the perspective of kernel coding standards, let’s look at
<span>typedef</span>
The kernel coding standards provide some scenarios for using<span>typedef</span>:
- Completely opaque objects: hiding internal objects
- Explicit integer types: abstraction helps avoid confusion about whether it is an int or long type, such as
<span>u8/u16/u32</span> - In certain special cases, new types that are the same as standard
<span>C99</span>types. - Types that can be used in user space
For more on kernel coding standards, see: https://www.kernel.org/doc/html/v4.10/process/coding-style.html
3. Personal Opinion
Personally, I feel that from the perspective of maintaining large projects,<span>typedef</span> is not recommended to avoid type proliferation, which also makes it harder to understand.
For small personal projects,<span>typedef</span> can be used at one’s discretion, as<span>typedef</span> has mixed reviews.
Here are some community discussion threads:
- Why we frequently use
<span>typedef</span>in the<span>C</span>language: https://stackoverflow.com/questions/252780/why-should-we-typedef-a-struct-so-often-in-c - Why the
<span>Linux</span>coding style guide discourages the use of<span>typedef</span>: https://www.reddit.com/r/C_Programming/comments/dan8vr/why_does_the_linux_kernel_coding_style_guide/?rdt=36702
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