C++ programming 2 min read

Arrays and strings

An array stores a fixed number of elements of one type, next to each other in memory. Firmware favours fixed-size arrays over dynamic containers: the size is known at compile time and nothing touches the heap.

int a[5] holds 10, 20, 30, 40 and 50 in five consecutive 4-byte cells from address 0x2000_0000; a[0] is the first. char s[6] = "Hello" holds H, e, l, l, o and a terminating zero character that marks the end of the string. — Arrays sit in consecutive memory; a C string ends with a zero.

A row of elements

Elements are numbered from 0, so an array of five ends at index 4. A range-based for visits each one without any index arithmetic.

array.cppC++

#include <iostream>int main() {    int a[5] = {10, 20, 30, 40, 50};    int sum = 0;    for (int value : a) {        sum += value;    }    std::cout << "first: " << a[0] << ", last: " << a[4] << ", sum: " << sum << '\n';}

Output

first: 10, last: 50, sum: 150

std::array and C strings

std::array<int, 3> is the same fixed block with a size() and bounds-checked .at(). A C string is a char array ending with '\0', which the compiler adds for you: "Hello" needs six characters.

strings.cppC++

#include <array>#include <cstring>#include <iostream>int main() {    char name[6] = "Hello";    std::array<int, 3> readings{4, 8, 15};    std::cout << name << " has " << std::strlen(name) << " letters" << '\n';    std::cout << "readings: " << readings.size() << '\n';}

Output

Hello has 5 letters
readings: 3