Why Does Loosely Checking `strpos()`'s Return Value Lead to Unexpected Results in PHP?

Unintended Consequence of Loosely Checking strpos() Return Value

When using strpos() to locate a substring within a string, it's essential to understand the potential pitfalls of using equality or inequality comparisons to evaluate its return value. While the PHP documentation states that strpos() returns false when the substring is not found, this can lead to unexpected results when it returns 0 (indicating the start of the string).

To illustrate this issue, consider the following code snippet:

if (
    strpos($grafik['data'], $ss1) <> false
    && strpos($grafik['data'], $ss2) <> false
    && strpos($grafik['data'], $ss1) < strpos($grafik['data'],$ss2)
)

The intention is to verify the presence of $ss1 and $ss2 within $grafik['data'] and ensure that $ss1 appears before $ss2. However, this does not account for the fact that strpos() returns 0 when $ss1 starts at the beginning of the string.

As per the PHP documentation:

Warning

This function may return Boolean FALSE, but may also return a non-Boolean value which evaluates to FALSE, such as 0 or "". Please read the section on Booleans for more information. Use the === operator for testing the return value of this function.

To address this issue, it is necessary to use the strict equality operator === instead of the loose equality operator ==.

if (
    strpos($grafik['data'], $ss1) !== false
    && strpos($grafik['data'], $ss2) !== false
    && strpos($grafik['data'], $ss1) < strpos($grafik['data'],$ss2)
)

By using ===, the comparison will correctly evaluate strpos()'s return value as true when the substring is found. This modification ensures the intended logical behavior of the code snippet.

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