I wanted to go “back to the basics” and try writing a C vector implementation.
It is using void* to store the data and i try to mimic the C++ counter part a little bit.

I am having difficulty erasing elements. precisely the size of the vector does not seem to match of whats expected after erasing multiple elements.

Here is the implementation of the erase function:

typedef void* vector_iterator;

vector_iterator vector_begin(vector* vec) {
    return vec->data;
}

vector_iterator vector_end(vector* vec) {
    return ((unsigned char*)vec->data) + ((vec->element_size * (vec->size+1))); // "past the last element"
}

void vector_erase(vector* vec, vector_iterator iterator) {
    assert(iterator >= vector_begin(vec));
    assert(iterator < vector_end(vec));
    assert(((uintptr_t)iterator - (uintptr_t)vector_begin(vec)) % vec->element_size == 0);
    unsigned char* dest = (unsigned char*)iterator;
    unsigned char* src = dest + vec->element_size; // src is the element erased element + 1, since we want to pull all objects forward
    size_t size_to_end = (unsigned char*)vector_end(vec) - (unsigned char*)src - vec->element_size;
    memcpy(dest, src, bytes_to_copy); // copy all elements from (iterator +1) forward
    vec->size--;
}

vector_iterator vector_iterator_offset(vector_iterator iterator,vector* vec, ptrdiff_t offset) {
    return (unsigned char*)iterator + (vec->element_size * offset);
}

The usage of erasing is used like this.

vector_erase(vec, vector_iterator_offset(vector_begin(vec),vec,2)); // erase the second element

When I erase 3 elements, the reported size of the vector is correct, but my loop prints size+1 elements.

    vector* vec = vector_create_capacity(sizeof(char), 10);
    //test for push back
    for(char i = 'A'; i < 'A'+10; ++i) {
        vector_push_back(vec, &i);
    }
    
    //...//
    
    fprintf(stdout, "Size: %zun",vector_size(vec));
    fflush(stdout);

    vector_erase(vec, vector_iterator_offset(vector_begin(vec),vec,2)); // erase 'C'
    fprintf(stdout, "Size: %zun",vector_size(vec));
    fflush(stdout);

    vector_erase(vec, vector_iterator_offset(vector_begin(vec),vec,2)); // erase 'D'
    fprintf(stdout, "Size: %zun",vector_size(vec));
    fflush(stdout);

    vector_erase(vec, vector_iterator_offset(vector_begin(vec),vec,2)); // erase 'E'
    fprintf(stdout, "Size: %zun",vector_size(vec));
    fflush(stdout);
    
    it = vector_begin(vec);
    for(;it != vector_end(vec); (it = vector_iterator_offset(it, vec, 1))) {
        
        char data = *(char*)it;
        fprintf(stdout,"%cn", data);
        fflush(stdout);
    }
    fprintf(stdout,"%zu",vector_size(vec));
    fflush(stdout);
    //8 printed letters instead of 7 with double 'J'?
    vector_destroy(vec);

Godbolt demo, because the code is very long

is my vector_end(vec) incorrect or is the erasing incorrect?