There are two ways to allocate memory to an array, of which the size is unknown at the beginning. The most common way is using malloc
like this
int * array;
... // when we know the size
array = malloc(size*sizeof(int));
But it's valid too in C99 to define the array after we know the size.
... // when we know the size
int array[size];
Are they absolutely the same?
The array is created at compile time while with malloc memory is allocated during run time; unless you grab all the memory with one malloc but then there is no advantage to using malloc.
Variable sized arrays are data structures whose length is determined at runtime rather than compile time. These arrays are useful in simplifying numerical algorithm programming. The C99 is a C programming standard that allows variable sized arrays.
Increasing the Array size in C Language: The following example demonstrates how to increase the array size in the C language. Here, we are using the malloc function to create the array in the heap memory and the free function to remove the unused memory.
So, the bottom line, you don't need to allocate any memory for the array. For each individual array elements, you need to allocate memory using memory allocator functions as you want each elements to point to valid memory.
No they're not absolutely the same. While both let you store the same number and type of objects, keep in mind that:
free()
a malloced array, but you can't free()
a variable length array (although it goes out of scope and ceases to exist once the enclosing block is left). In technical jargon, they have different storage duration: allocated for malloc versus automatic for variable length arrays.malloc
allocates from the heap. This is an issue on stack-limited systems, e.g. many embedded operating systems, where the stack size is on the order of kB, while the heap is much larger.malloc
than with a variable length array.realloc()
, while VLAs can't (more precisely only by executing the block again with a different array dimension--which loses the previous contents).malloc()
.__STDC_NO_VLA__
as the integer 1 according to C11 6.10.8.3).If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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