When is dynamic memory allocation more suitable

The prototype for the standard library function is like this:. The free function takes the pointer returned by malloc and de-allocates the memory. No indication of success or failure is returned. The function prototype is like this:.

The pointer de-referencing syntax is hard to read, so normal array referencing syntax may be used, as [ and ] are just operators:. Assigning NULL to the pointer is not compulsory, but is good practice, as it will cause an error to be generated if the pointer is erroneous utilized after the memory has been de-allocated.

The amount of heap space actually allocated by malloc is normally one word larger than that requested. The additional word is used to hold the size of the allocation and is for later use by free. The calloc function does basically the same job as malloc , except that it takes two parameters — the number of array elements and the size of each element — instead of a single parameter which is the product of these two values.

The allocated memory is also initialized to zeros. Here is the prototype:. The realloc function resizes a memory allocation previously made by malloc. It takes as parameters a pointer to the memory area and the new size that is required. If the size is reduced, data may be lost. If the size is increased and the function is unable to extend the existing allocation, it will automatically allocate a new memory area and copy data across.

In any case, it returns a pointer to the allocated memory. The new operator can be used in three ways:. In the first two cases, space for a single object is allocated; the second one includes initialization. The third case is the mechanism for allocating space for an array of objects. The first is for a single object; the second deallocates the space used by an array.

It is very important to use the correct de-allocator in each case. Again, assigning NULL to the pointer after deallocation is just good programming practice. This may be inadvisable for real time embedded systems. As a general rule, dynamic behavior is troublesome in real time embedded systems.

The two key areas of concern are determination of the action to be taken on resource exhaustion and nondeterministic execution performance. There are a number of problems with dynamic memory allocation in a real time system.

The standard library functions malloc and free are not normally reentrant, which would be problematic in a multithreaded application. If the source code is available, this should be straightforward to rectify by locking resources using RTOS facilities like a semaphore. A more intractable problem is associated with the performance of malloc.

Its behavior is unpredictable, as the time it takes to allocate memory is extremely variable. Such nondeterministic behavior is intolerable in real time systems.

Without great care, it is easy to introduce memory leaks into application code implemented using malloc and free. This is caused by memory being allocated and never being deallocated. Such errors tend to cause a gradual performance degradation and eventual failure. This type of bug can be very hard to locate. Memory allocation failure is a concern.

Unlike a desktop application, most embedded systems do not have the opportunity to pop up a dialog and discuss options with the user. Often, resetting is the only option, which is unattractive. If allocation failures are encountered during testing, care must be taken with diagnosing their cause. It may be that there is simply insufficient memory available — this suggests various courses of action.

However, it may be that there is sufficient memory, but not available in one contiguous chunk that can satisfy the allocation request. At a later point you would need to manually free the memory. Thanks for the input. I changed the code, so that it is in a function. Now we really need a heap allocation, because otherwise it goes out of scope when leaving createPeople — x squared. To get an idea of how big the stack is see this page. Note that the actual stack size may differ.

C passes arguments, and returns values by value. If you want to return an array, which decays into a pointer, you'll end up returning a pointer to an array that is out of scope invalid , resulting in UB. Functions like these should allocate memory and return a pointer to it.

When you need to change the size of something realloc , or you don't know how much memory you'll need to store something. In certain cases globals won't do think threading. Besides: globals are in almost all cases regarded as bad practice. Shared libs generally use heap memory.

This is because their authors can't assume that their code will have tons of stack space readily available. Beta Carotin Beta Carotin 1, 1 1 gold badge 9 9 silver badges 25 25 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete? Podcast Do polyglots have an edge when it comes to mastering programming Featured on Meta.

Now live: A fully responsive profile. Linked 0. Related 0. Resources are always a premium. We have strived to achieve better utilization of resources at all times; that is the premise of our progress. Related to this pursuit, is the concept of memory allocation. Memory has to be allocated to the variables that we create, so that actual variables can be brought to existence. Now there is a constraint as how we think it happens, and how it actually happens.

How computer creates a variable? This example probably made it very clear as how the computer does the allocation of memory. Now, what is Static Memory Allocation? When we declare variables, we actually are preparing all the variables that will be used, so that the compiler knows that the variable being used is actually an important part of the program that the user wants and not just a rogue symbol floating around.

So, when we declare variables, what the compiler actually does is allocate those variables to their rooms refer to the hotel analogy earlier. Why would we need to allocate memory while the program is executing? So, as we have been going through it all, we can tell that it allocates the memory during the run time which enables us to use as much storage as we want, without worrying about any wastage.