How to cout a vector in C++

In this article, we will discuss how to print a vector using std::cout in C++.

By default we can directly pass a vector object to the cout in C++. As, ‘cout’ calls the operator<<() function of each passed object. So, we can overload a operator<< function of vector like this,

#include <iostream>
#include <vector>

/*
Overload the << operator to print a vector object
*/
template <typename T>
std::ostream& operator<<(
                std::ostream& outputStream,
                const std::vector<T>& vectorObj)
{
    // Print all the elements of vector using loop
    for (auto elem : vectorObj)
    {
        outputStream<< elem << " ";
    }
    return outputStream;
}

It is a template function, that accepts any kind of vector, and uses a for loop to print the vector contents. Once this function is defined, then we can directly pass a vector object to console. Like this,

// create a vector, and initialize with 10 integers
std::vector<int> vectorObj {11, 12, 13, 14, 15, 16, 17, 18, 19, 20}; 

// display vector on console
std::cout << vectorObj << std::endl;

It will print the contents of vector like this,

11 12 13 14 15 16 17 18 19 20 

This technique will work for any type of vector object. We can use this to print a vector strings with std::cout. Like this,

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std::vector<std::string> vecOfStrs {"Hi", "this", "is", "from", "a", "vector"};

// display vector on console
std::cout << vecOfStrs << std::endl;

It will print the contents of vector like this,

Hi this is from a vector

This way we can print all elements of a vector by directly using the std::cout. Let’s see a complete example, where we will print all the contents of vector by just passing it to cout.

#include <iostream>
#include <vector>

/*
Overload the << operator to print a vector object
*/
template <typename T>
std::ostream& operator<<(
                std::ostream& outputStream,
                const std::vector<T>& vectorObj)
{
    // Print all the elements of vector using loop
    for (auto elem : vectorObj)
    {
        outputStream<< elem << " ";
    }
    return outputStream;
}

int main ()
{
    // create a vector, and initialize with 10 integers
    std::vector<int> vectorObj {11, 12, 13, 14, 15, 16, 17, 18, 19, 20}; 

    // display vector on console
    std::cout << vectorObj << std::endl;

    std::vector<std::string> vecOfStrs {"Hi", "this", "is", "from", "a", "vector"};

    // display vector on console
    std::cout << vecOfStrs << std::endl;

    return 0;
}

Output:

11 12 13 14 15 16 17 18 19 20 
Hi this is from a vector 

So, today we learned how to print a vector using std::cout in C++. Thanks.

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Thanks for reading.

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