Rather than get burned again they are moved into the never use category. Instead developers should make sure that they completely understand how to use the feature, what precautions are needed for proper use, how to recover in the event the worst case happens and then of course proper testing to ensure that everything goes according to plan. One concept whose use is not rooted in the advancement of compiler technology or hardware advances is the use of features that are ambiguously defined in the C standard.
A great example of such a feature is a bit field. The biggest problem with using bit fields is that there are usually portability issues. There are also issues with padded bytes being added to the overall structure. A great example of using bit fields is for creating a structure that is used to create a configuration table for initializing a driver or application.
Standards and best practices are designed to help prevent developers from shooting themselves in the foot, but they are just that, best practices. A standard may say that the use of a C feature is forbidden but the fact of the matter is that it is up to the developer in his or her own unique situation to determine whether conventional wisdom applies. Challenging our preconceptions and ensuring we understand why those best practices are in place is just as important as following them. What other features have you encountered that work in todays development environment but traditionally been considered forbidden?
It is not obvious to me why memset should be a particular problem. Ok maybe if dynamic memory management is involved. Otherwise it is similar to writing to an array. Thanks for clarifications. Fairly trivial but something that is now picked up by C compilers which was not picked up in the past. As long as you are careful with: — Not comparing floats for equality i.
I think that using floats is less prone to errors than scaled arithmetic. I still believe you should avoid malloc because however much RAM you have, fragmentation will happen most likely in the field, not the lab. If used in an RTOS environment, you have to be careful about reentrancy.
Compiler vendors typically optimize memset , though. In addition, almost every embedded systems programming standard bans dynamic memory allocation. Improve this answer. Community Bot 1 1 1 silver badge. Lundin Lundin k 35 35 gold badges silver badges bronze badges. Being "explained" elsewhere on the Internet does not make it true. The example you referenced is a system wuth 4kb of RAM. Not all embedded systems are of that nature. There are many reasons not to use dynamic memory allocation in some embedded systems, but you have to understand those reasons, and the constraints and requirements of your particular system to make an informed decision rather than follow some ill understood dogma.
Moreover I would suggest "many embedded systems programming standards" rather the "almost all" - that would be hard to back up evidentially even if it were true — Clifford. Add a comment. There is nothing specific about embedded systems that prevent the use of dynamic memory. However you may need to provide support for it in a number of ways, for example: You need to ensure that the linker allocates sufficient space for the dynamic heap.
Some linker scripts may already automatically allocate all remaining memory to the heap after stack and any other reserved allocations. In a multi-threaded system you may need to implement mutex stubs to ensure safe heap allocation. There are a number of reasons however why you might choose to avoid using dynamic memory or at least standard library implemented dynamic memory in an embedded system however: Standard allocation schemes have non-deterministic timing unsuited to hard-real-time systems.
You need to handle the possibility of allocation failure gracefully for every allocation. Handling a potential non-deterministic run-time error safely is more complex than simply having the compiler tell you have insufficient memory at build time.
You need to guard against memory leaks; true of any system, but with no OS to manage memory exhaustion and kill a leaking process how will your system behave? The standard library heap management may not be thread-safe without mutex stubs or wrapper functions. Bugs that corrupt the heap are unlikely to affect execution immediately, often only causing an observable failure when a new heap operation is performed, resulting in non-deterministic behaviour at a time and location unrelated to the actual cause - making them very hard to diagnose.
Again this is true of any system, but the debug facilities in a cross-hosted embedded system are often less sophisticated that on a self-hosted system. Clifford Clifford Also consider memory fragmentation. Technophile : Ultimately fragmentation is a cause of both non-deterministic timing and allocation failure.
I chose not to highlight it separately; what I have listed are issues of dynamic allocation rather the the causes of those issues. Zhifei Zhifei 5 5 bronze badges. Sign up or log in Sign up using Google. I am working since 0.
I never used malloc in 8-bit controller programming. In embedded systems the use of dynamic allocation is strongly discouraged. Behavior of the critical systems should be deterministic. Many libraries and OS for embedded firmware avoid using dynamic allocation. For short explanation why malloc is not good for embedded systems see: malloc sins. No it is not useful. The whole purpose of malloc is to let multiple processes share all available RAM memory of the system dynamically, when they have need for it.
This in turn implies that you have a multi-process system and that the amount of available RAM is vast, but also variable or unknown. In smaller embedded systems that are either "bare metal" no OS or use a RTOS, such memory sharing does not make any sense. Unlike a PC, such an embedded system is completely deterministic and therefore you always know the amount of RAM needed for the worst case.
You also know exactly how much RAM there is on the chip. The need of using malloc on such systems typically originates from confused PC programmers who have picked up embedded programming without studying it first. Details here. When you do your system engineering that includes the allocation of resources. Being a single task, that one task owns all the resources in the system.
So it is at design time that you determine how much of each you need, including memory. Long long before runtime you already know what structures get how much memory, so there is no reason to add the risk of that extra code for something you already know the answer to. If you have been doing this for 5 years then you already know this.
If you have not been doing your system engineering, then you should start seeing your past work starting to fail in the field. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow.
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