C ++ Arrays, std :: array, std :: vector summary

Original from: https://shendrick.net/Coding%20Tips/2015/03/15/cpparrayvsvector.html @Seth Hendrick
Original Article This article was: https://shendrick.net/Coding%20Tips/2015/03/15/cpparrayvsvector. html @Seth Hendrick

C-Style Array

Assignment

int myArray[3] = {1, 2, 3};

Arrays and pointers

a[1]Equivalent to*(a+1)

std::cout << std::boolalpha << (myArray[0] == *myArray) << std::endl;
std::cout << std::boolalpha << (myArray[1] == *(myArray + 1) << std::endl;

// Outputs:
// true
// true

Array size

int myArray[5] = {1, 2, 3, 4, 5};
size_t arraySize = sizeof(myArray) / sizeof(int);
std::cout << "C-style array size: " << arraySize << std::endl;
// Outputs:
// C-style array size: 5

#include <iostream>

void printSize(int someArray[5]) {
    std::cout << sizeof(someArray)/sizeof(int) << std::endl;
}

int main() {
    int myArray[5] = {1, 2, 3, 4, 5};
    printSize(myArray);
}

// Outputs:
// 2

The second example, the function does not return the correct size of the array. This is because the array as an input parameter, is passed in a size_tsize of a pointer, in particular the size of the machine may be 8 bytes, the inttype size is four words section, since the second example corresponds to sizeof(size_t) / sizeof(int)the output 2 of the result.

Traversal cycle

A section similar to the above, in the same scope, the array can be in C ++ through the loop 11,

int main() {
   int myArray[5] = {1, 2, 3, 4, 5};
   for (int &i : myArray) {
       std::cout << i << ", " << std::endl;
   }
}

But when the array is passed as a function of other variables, failed traversal cycle

#include <iostream>

void printElements(int someArray[5]) {
    for (int &i : someArray) {
        std::cout << i << ", " << std::endl;
    }
}

int main() {
    int myArray[5] = {1, 2, 3, 4, 5};
    printElements(myArray);
}

The reason is the same, is passed a pointer.

std::array

std::arrayC is an array after a package, you must determine the size of the array at compile time.

Declare an array

#include <array>
#include <iostream>

void printElements(const std::array<int, 5> &someArray) {
    for (const int &i : someArray) {
        std::cout << i << ", " << std::endl;
    }

    std::cout << "Size: " << someArray.size() << std::endl;
}

int main() {
    std::array<int, 5> myArray = {1, 2, 3, 4, 5};
    printElements(myArray);
}

// Outputs:
// 1,
// 2,
// 3,
// 4,
// 5,
// Size: 5