Why do we need to use malloc() or any other Dynamic Memory for ARRAYS in C?

what is dynamic memory allocation in c
the malloc() function in c/c++ allocates memory at which time/location
static memory allocation in c
dynamic memory allocation in c programming examples
c malloc array
difference between malloc and calloc
malloc vs calloc
dynamic memory allocation in data structure

Consider these codes in C:

int n;  
scanf("\n%d ",&n);  
int arr[n];

and this.

int n;
scanf("\n%d ",&n);
int *p = (int *)malloc(n*sizeof(int));  

Why do we need dynamic memory allocation for this in the first place? and is the first code not Dynamic Memory Allocation as the array is created during runtime?

When should I use malloc()?

int arr[n]; allocates memory on the stack. It is automatically allocated and then deallocated at the end of the block. A pointer to stack memory cannot be safely returned from a function.

Consider this.

#include <stdio.h>

char *make_array() {
    int n;  
    scanf("%d",&n);

    // Memory for `arr` is allocated on the stack.
    char arr[n];

    // And then deallocated when the function exits.
    // A good compiler and editor will warn you if you try
    // to return it.
    return arr;
}

int main() {
    // This pointer is to memory which has already been freed. Other things
    // will overwrite it.
    char *arr = make_array();

    arr[0] = 'c';
    arr[1] = '\0';

    // This could be the letter c, but it's probably gibberish.
    puts(arr);
}

If you need memory to live beyond the life of the current function, you need to allocate it on the heap with malloc and manage it yourself.

Why do we need to use malloc() or any other Dynamic Memory for , malloc() allocates memory "upon request" from a different area called "the The "C" language conveniently allows you to use "array notation"� C realloc() method “realloc” or “re-allocation” method in C is used to dynamically change the memory allocation of a previously allocated memory. In other words, if the memory previously allocated with the help of malloc or calloc is insufficient, realloc can be used to dynamically re-allocate memory. re-allocation of memory maintains the already present value and new blocks will be

Just to be sure you understand:

When "functions call functions," their local variables are stored in an area of memory known as "the stack," so named because it works like a push-down LIFO stack. When a function is entered, the stack grows. When the function returns, it shrinks. And if a function recursively calls itself, there's no confusion because each instance has its own area on the stack.

malloc() allocates memory "upon request" from a different area called "the heap," so named because it has no particular built-in organization. These areas of memory are referenced indirectly, using "pointers," which are variables whose value is understood to be a memory address.

The "C" language conveniently allows you to use "array notation" when using pointers, just as it does with local variables that are allocated on the stack.

malloc in C: Dynamic Memory Allocation in C Explained, malloc() is a library function that allows C to allocate memory malloc() is part of stdlib.h and to be able to use it you need to use #include <stdlib.h> . Here we'll make a pointer to a soon-to-be array of ints int* arrayPtr;. Unlike other languages, C does not know the data type it is allocating memory for;� Keep in mind that the allocated memory is contiguous and it can be treated as an array. We can use pointer arithmetic to access the array elements rather than using brackets [ ]. We advise to use + to refer to array elements because using incrementation ++ or += changes the address stored by the pointer.

int n;  
scanf("\n%d ",&n);  
int arr[n];

If it works then that means you are using compiler that still interprets it as "DMA" the only difference here would be that it will get deallocated at the end of the scope but I don't think it's a good practice for C.

C Dynamic Memory Allocation using malloc(), calloc(), realloc(), free(), When you declare a variable using a basic data type, the C compiler automatically in which the array size is undecided until you run your program ( runtime). robust when *ptr declaration is typecasted to a different data type later . In dynamic memory allocation, you have to deallocate memory explicitly. C malloc() The name "malloc" stands for memory allocation. The malloc() function reserves a block of memory of the specified number of bytes. And, it returns a pointer of void which can be casted into pointers of any form.

int n;  
scanf("\n%d ",&n);  
int arr[n];

where the n is a runtime-dynamic value (as it is in this case) was not supported in older versions of C, which required that the n be an integer constant expression.

Modern versions of C have lifted this limitation, allowing dynamically sized arrays (variable length arrays, or VLAs), but unlike the old fixed-sized arrays, VLAs have restrictions.

They aren't allowed to be jumped across (with break/continue/goto), they might not be be async-signal-safe, they will crash your program if they get too large, and they will often generate larger code than plain old local arrays.

Also, because they're local, you can't return a pointer to them to your caller.

The size limitations is one of their biggest restrictions. VLAs are carved out of the call stack, which is typically only a couple of kilo/mega-bytes large, and you get a typically undiagnosed crash if you exceed this limit.

malloc'd memory doesn't have such a limit, malloc failures are clearly reported via a returned NULL, and because malloc'd memory is global to the process, you can pass a pointer to it back to your caller.

`

C dynamic memory allocation, C dynamic memory allocation refers to performing manual memory management for dynamic In C, the library function malloc is used to allocate a block of memory on the When the program no longer needs the dynamic array, it must eventually call With realloc we can resize the amount of memory a pointer points to. The C library function void *malloc(size_t size) allocates the requested memory and returns a pointer to it. Declaration. Following is the declaration for malloc() function. void *malloc(size_t size) Parameters. size − This is the size of the memory block, in bytes. Return Value

Arrays in C, Dynamically declared 2D arrays can be and have an array of column arrays. (int *)malloc(sizeof(int)*N*M); // in memory: // row use [i][j] syntax because the compiler j++) { arr[i*cols +j] = 0; } } } int main() which is different from the Method 1� In this article, I am going to discuss Dynamic Memory Management in C. It is a procedure of allocating or de-allocating the memory at run time

C Dynamic Memory Allocation Using malloc(), calloc(), free , Dynamically allocated memory created with either calloc() or malloc() doesn't get freed on their own. You must explicitly use free() to release the space. Syntax of� This is because fun() makes a copy of the pointer, so when malloc() is called, it is setting the copied pointer to the memory location, not p. p is pointing to random memory before and after the call to fun(), and when you dereference it, it will crash.

Dynamic memory allocation in C : calloc, malloc, free, realloc in C, Learn dynamic memory allocation in C. Learn to use calloc, malloc, free, realloc C also when we want to input a sentence as an array of characters but are not sure #include <stdio.h> #include <stdlib.h> #include <string.h> int main() { char a pointer of type void but we can typecast it into a pointer of any other form (as � "Unless you are forced to use C, you should never use malloc. Always use new." Why? What is the win here? For objects we need construction, but for memory blocks, you clearly document two ways to make coding mistakes (the more easily caught vs [] in new and the less easily caught mismatched array vs scaler new and delete).

Comments
  • For this.. - for what? This program is not doing anything. And as a side note, DMA is more commonly known for being "Direct Memory Access".
  • Any good C textbook or tutorial will explain why dynamic memory allocation is needed.
  • For example, you need to use malloc() if the array needs to persist after the function returns.
  • The first version uses a relatively modern feature of C standard: variable length arrays, or VLAs for short. The original C standard from 1990 did not have VLAs, but the updated C standard in 1999 defined them. In the later updated C standard from 2011, support for VLAs was made optional. The advantage of VLAs is that you don't need to free them. The disadvantage of VLAs is that they might result in a stack overflow error that cannot be handled gracefully (within the confines of the C standard).
  • Arrays of variable length did not exist before C99. In many cases you can use one or the other to implement what you want to achieve. There are differences, so both have advantages and you would choose one or the other in different cases. (A question why you can choose between different tools is difficult to answer.)
  • you mean after I have exited the program, the array is destroyed? and malloc isn't until we use free()?
  • No, array is destroyed at the end of the scope {your scope}
  • But if you leave some allocated memory your OS should deallocate it automatically after you exit your application but that's also a bad practice...
  • @AyushBasak memory allocated by malloc should be reclaimed by the operating system automatically when the process exits, but it is generally considered good practice to free such memory explicitly before exiting the process. A program should definitely not keep "forgetting" to free stale memory blocks while allocating replacement memory blocks in an ad hoc manner. That's a "memory leak".