Question

I’m looking at Webmonkey’s PHP and MySql Tutorial, Lesson 2. I think it’s a php literal. What does %s mean? It’s inside the print_f() function in the while loops in at least the first couple of code blocks.

printf("<tr><td>%s %s</td><td>%s</td></tr>n", ...

Answer 1

with printf or sprintf characters preceded by the % sign are placeholders (or tokens). They will be replaced by a variable passed as an argument.

Example:

$str1 = 'best';
$str2 = 'world';

$say = sprintf('Tivie is the %s in the %s!', $str1, $str2);
echo $say;

This will output:

Tivie is the best in the world!

Note: There are more placeholders (%s for string, %d for dec number, etc…)

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Order:

The order in which you pass the arguments counts. If you switch $str1 with $str2 as

$say = sprintf('Tivie is the %s in the %s!', $str2, $str1); 

it will print

“Tivie is the world in the best!”

You can, however, change the reading order of arguments like this:

$say = sprintf('Tivie is the %2$s in the %1$s!', $str2, $str1);

which will print the sentence correctly.

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Also, keep in mind that PHP is a dynamic language and does not require (or support) explicit type definition. That means it juggles variable types as needed. In sprint it means that if you pass a “string” as argument for a number placeholder (%d), that string will be converted to a number (int, float…) which can have strange results. Here’s an example:

$onevar = 2;
$anothervar = 'pocket';
$say = sprintf('I have %d chocolate(s) in my %d.', $onevar, $anothervar);
echo $say;

this will print

I have 2 chocolate(s) in my 0.

More reading at PHPdocs