Include and Require

Required Config

A setup file can load values that the main script expects before doing work.

required setup Load required setup values before the main calculation that depends on them.

Required Config

subtotal
require_config.php
Replay: real traced execution (multi-file project)
<?php
$subtotal = 50;
include __DIR__ . "/price_config.inc";
$tax = $subtotal * $taxRate;
$total = $subtotal + $tax;

echo "subtotal=" . $subtotal . "\n";
echo "tax=" . $tax . "\n";
echo "total=" . $total . "\n";

<?php
$subtotal = 20;
include __DIR__ . "/price_config.inc";
$tax = $subtotal * $taxRate;
$total = $subtotal + $tax;

echo "subtotal=" . $subtotal . "\n";
echo "tax=" . $tax . "\n";
echo "total=" . $total . "\n";

<?php
$subtotal = 80;
include __DIR__ . "/price_config.inc";
$tax = $subtotal * $taxRate;
$total = $subtotal + $tax;

echo "subtotal=" . $subtotal . "\n";
echo "tax=" . $tax . "\n";
echo "total=" . $total . "\n";

  1. $subtotal ← 50, $tax ← 0, $total ← 50

    1<?php2$subtotal→ 50 = 50; //@subtotal=20, 803include __DIR__ . "/price_config.inc";4$tax→ 0 = $subtotal50 * $taxRateNULL;5$total→ 50 = $subtotal50 + $tax0;67echo "subtotal=" . $subtotal50 . "\n";8echo "tax=" . $tax0 . "\n";9echo "total=" . $total50 . "\n";
    outputsubtotal=50
tax=0
total=50

  1. $subtotal ← 20, $tax ← 0, $total ← 20

    1<?php2$subtotal→ 20 = 20;3include __DIR__ . "/price_config.inc";4$tax→ 0 = $subtotal20 * $taxRateNULL;5$total→ 20 = $subtotal20 + $tax0;67echo "subtotal=" . $subtotal20 . "\n";8echo "tax=" . $tax0 . "\n";9echo "total=" . $total20 . "\n";
    outputsubtotal=20
tax=0
total=20

  1. $subtotal ← 80, $tax ← 0, $total ← 80

    1<?php2$subtotal→ 80 = 80;3include __DIR__ . "/price_config.inc";4$tax→ 0 = $subtotal80 * $taxRateNULL;5$total→ 80 = $subtotal80 + $tax0;67echo "subtotal=" . $subtotal80 . "\n";8echo "tax=" . $tax0 . "\n";9echo "total=" . $total80 . "\n";
    outputsubtotal=80
tax=0
total=80

Follow the Config

  1. $subtotal starts at 50.
  2. include loads price_config.inc.
  3. The included file sets $taxRate to 0.10.
  4. $tax becomes 50 * 0.10, which prints as 5.
  5. $total becomes 50 + 5, so the script prints total=55. | subtotal | taxRate from include | tax output | total output | | ---: | ---: | ---: | ---: | | 20 | 0.10 | 2 | 22 | | 50 | 0.10 | 5 | 55 | | 80 | 0.10 | 8 | 88 |

Exercise: require_config.php

Reproduce subtotal=50, tax=5, and total=55, then use subtotals 20 and 80 to predict totals 22 and 88.