how to center columns in bootstrap code example

Example 1: bootstrap col center content

<div class="row">
    <div class="col-4 d-flex justify-content-center text-center">
        // for image and text
    </div>
</div>

Example 2: bootstrap 4 center div

<div class="d-flex justify-content-start">...</div>
<div class="d-flex justify-content-end">...</div>
<div class="d-flex justify-content-center">...</div>
<div class="d-flex justify-content-between">...</div>
<div class="d-flex justify-content-around">...</div>

Example 3: bootstrap center align columns

<!-- Center columns in a Row -->
<div class="row d-flex justify-content-center text-center">
    <div class="col-4">
        // Add Content
    </div>
    <div class="col-4">
        // Add Content
    </div>
    <div class="col-4">
        // Add Content
    </div>
</div>

Example 4: columns center bootstrap 3

<div class="row">
    <div class="col-md-2 col-md-offset-5"></div>
</div>