Dynamic Array and std::vector
A dynamic array keeps a logical size separate from allocated capacity and reallocates geometrically.
What is Dynamic Array and std::vector?
A dynamic array keeps a logical size separate from allocated capacity and reallocates geometrically.
Grow contiguous storage as values are appended.
Important points
- State the invariants before implementing operations.
- Handle empty, full, and allocation-failure cases.
- Measure time complexity and memory ownership together.
C and C++ code examples
main.c
#include <stdio.h>
#include <stdlib.h>
int main(void) {
size_t size = 0, capacity = 2;
int *values = malloc(capacity * sizeof *values);
if (!values) return 1;
for (int value = 1; value <= 5; ++value) {
if (size == capacity) {
capacity *= 2;
int *grown = realloc(values, capacity * sizeof *values);
if (!grown) {
free(values);
return 1;
}
values = grown;
}
values[size++] = value * value;
}
printf("size=%zu capacity=%zu last=%d\n",
size, capacity, values[size - 1]);
free(values);
}
size=5 capacity=8 last=25C++
main.cpp
#include <iostream>
#include <vector>
int main() {
std::vector<int> values;
for (int value = 1; value <= 5; ++value) {
values.push_back(value * value);
}
std::cout << "size=" << values.size()
<< " last=" << values.back() << '\n';
}
size=5 last=25C and C++ comparison
The C version explicitly checks realloc and updates capacity. std::vector packages the same growth strategy with automatic destruction, iterators, and exception safety.
C
Structures and operations are usually separate and allocation is explicit.
C++
Classes and containers can preserve invariants and manage resources automatically.
Practice exercises
Run both versions, then modify them to observe the different language guarantees.
- Add empty and capacity-boundary tests.
- Implement cleanup and verify no leaks remain.
- Compare operation complexity with a standard container.