从C中的动态数组中的特定位置删除元素

Question

I'm having some trouble wrapping my head around pointers and memory management in C.

In this particular instance, I'm trying to delete an element from within a dynamically allocated array.

Consider the following lines of code:

void deleteElemFromPosition(VectorDinamic *v, unsigned int poz){
int nCap = v->capacity;
Element* nElems = malloc(nCap * sizeof(Element));

int i;
for (i = 0; i < v->lg; i++) {
    if(i!=poz)nElems[i] = v->elems[i];
    else{
            nElems[i]=v->elems[i+1];
            ++i;

    }
}

free(v->elems);
v->elems = nElems;
v->capacity = nCap;
}

This piece creates a copy of the array that I'm trying to copy with one difference. It doesn't store the element at the wanted position, but rather than doing so, it seems to enter an infinite loop, or actually, not infinite but very very big. So big that it makes the program crash.

Any kind of help would be appreciated.

EDIT: Maybe I should have included the definition of the dynamic array from the beginning. Oh well.

VectorDinamic * creazaVectorDinamic() {
VectorDinamic *v = malloc(sizeof(VectorDinamic));
v->elems = malloc(INIT_CAPACITY * sizeof(Element));
v->capacitate = INIT_CAPACITY;
v->lg = 0;
return v;

Answer 1

You have several problems. For a start:

1. You do not need to malloc() a completely new array then copy things in. Just shuffle down the ones above the element you are deleting using memmove , then realloc to shrink the allocated memory.

2. Your loop increments i twice, once in the for loop, and once in the else clause.

3. There seems to be some confusion between v->capacity and v->lg . What is the difference between these two?

In general, telling us where and how it crashes would be useful, as would the definition of VectorDinamic (note dynamic is spelt thus). Try using gdb or similar.

Answer 2

In this way is very difficult to find the bug. There could be multiple elements that makes your program crash, like the malloc(nCap * sizeof(Element)) that can return null on error, or free(v->elems); if v->elems is statically allocated or if null . We don't know what is v->lg ... Try to debug with gdb or valgrind .