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Comments on What are disadvantages of static functions (ie functions with internal linkage) in C?
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What are disadvantages of static functions (ie functions with internal linkage) in C?
Functions in C have external linkage by default. In other words, the storage class specifier extern is applied to functions by default, with the effect that they are visible to all translation units.
The storage class specifier static gives functions internal linkage and restricts visibility to the given translation unit.
Some comparison to other programming languages is instructive:
- In Java, one is taught from early on to give thought to the right choice of access modifier, which in most cases means choosing between
publicandprivate. - In Pascal, one can define functions (and procedures, ie functions without a return type) within other functions (or procedures). However in C, functions can only be defined at file scope, giving them global visibility by default (and thereby making us have to worry about internal vs external linkage).
Restricting visibility is a good thing. But I have encountered relatively few functions marked static in production code, even though they could have been given internal linkage. We can therefore ask: What are disadvantages of static functions (ie functions with internal linkage) in C?
An admittedly opinion-based way of asking would be: Why aren't static functions used much more widely in C? (The answer might simply be "traditionally people don't bother to change the default linkage for functions from external to internal".)
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Besides what Olin already said, I guess too many people were taught C using K&R book, which was great at the time, but it completely neglects modern SW engineering best practices (encapsulation, data hiding, modularization, etc.), many of which were popularized to the wider programmer audience by C++ and later by Java, since these languages support OOP and in this paradigm modularization (which static in C is for) is essentially a must (in C++ you have namespaces, classes and all sort of mechanism to do so).
In particular, separation of the interface of a module from the implementation is essentially made using static vs extern functions: write the interface in a header file where you declare all the public functions the module must export, then include the header in the corresponding source file (.c file) where you implement the public functions using all the private (static) helper functions you need.
One of the staple of good SW design is to avoid fat interfaces, i.e. interfaces with a lot of functions that don't need to be public, but are there "just in case". C programmers that cram their headers with all the functions in their modules probably haven't been exposed to OOP languages or are too inexpert in modern C programming practices (you can do OOP even in C, but it requires quite a lot of discipline since the language won't help you there)
Another alternative is that they are "old timers" that grew up with assembly and C at low level, where legacy code written for "bare metal" systems didn't need too much SW engineering best practices to work well. After all, if all you have is an MCU with 16k or so of Flash and some kiBs of RAM (and you are a good programmer) you can write pretty good software even using C as an higher level assembly.
The problem is that this doesn't scale well for bigger systems. Once your project code base size hits the thousands of source code lines of C you are in for very nasty surprises if you don't employ higher level techniques, and one of the most basic techniques is using static to compartmentalize functions in the module they belong to.
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