The m[line][column] = 12 syntax is ok (provided line and column are in range). However, you didn’t write the code you use to allocate it, so it’s hard to get whether it is wrong or right. It should be something along the lines of m = (int**)malloc(nlines * sizeof(int*)); for(i = 0; i < nlines; … Read more
As far as I can tell, it seems like that code is still trying to allocate the array on the stack first, and then move it into the box after. It works for me if I switch to Vec<f64> in place of Box<[f64]> like this: fn new_gap(gap: usize) -> usize { let ngap = ((gap … Read more
You need to use dynamic memory when: You cannot determine the maximum amount of memory to use at compile time; You want to allocate a very large object; You want to build data structures (containers) without a fixed upper size; You don’t always know how much memory you will need to set aside at compile … Read more
Yes, automatic variables will be destroyed at the end of the enclosing code block. But keep reading. Your question title asks if a destructor will be called when the variable goes out of scope. Presumably what you meant to ask was: will Foo’s destructor be called at the end of main()? Given the code you … Read more
malloc is used for dynamic memory allocation. As said, it is dynamic allocation which means you allocate the memory at run time. For example when you don’t know the amount of memory during compile time. One example should clear this. Say you know there will be maximum 20 students. So you can create an array … Read more
Static arrays are created on the stack, and have automatic storage duration: you don’t need to manually manage memory, but they get destroyed when the function they’re in ends. They necessarily have a fixed size at compile time: int foo[10]; Arrays created with operator new[] have dynamic storage duration and are stored on the heap … Read more
Just don’t call free() on your original ptr in the happy path. Essentially realloc() has done that for you. ptr = malloc(sizeof(int)); ptr1 = realloc(ptr, count * sizeof(int)); if (ptr1 == NULL) // reallocated pointer ptr1 { printf(“\nExiting!!”); free(ptr); exit(0); } else { ptr = ptr1; // the reallocation succeeded, we can overwrite our original … Read more
This is a standard interview question: Dynamic memory allocation Is memory allocated at runtime using calloc(), malloc() and friends. It is sometimes also referred to as ‘heap’ memory, although it has nothing to do with the heap data-structure ref. int * a = malloc(sizeof(int)); Heap memory is persistent until free() is called. In other words, … Read more
My recommendation is to consider your matrix as having some abstract data type that you want to implement. A common way might be to use an array of pointers (to arrays representing rows of your matrix). But I feel it is confusing and inefficient. So what are the operations you want on your matrixes? create … Read more
The reason for this bug is that the data used by the create_array function is a local variable that only exists inside that function. The assigned memory address obtained from malloc is only stored in this local variable and never returned to the caller. Consider this simple example: void func (int x) { x = … Read more