Common errors in using is_nan function and their solutions

During PHP programming, the is_nan function is often used to determine whether a value is a "non-number" (NaN, Not-a-Number). Its function is usually to check if a variable is "not a valid number", especially when doing mathematical calculations, it is very useful. However, in actual development, many developers may encounter errors in using is_nan function. This article will analyze common usage errors for you and provide solutions.

1. Basic usage of is_nan

The is_nan function is used to check whether a value is NaN (Not-a-Number). The function prototype is as follows:

 bool is_nan ( mixed $val )

• Parameter $val : The value to be checked.

• Return value: true if $val is NaN , otherwise false .

Example:

 $val = 0 / 0; // turn out NaN
if (is_nan($val)) {
    echo "yes NaN";
} else {
    echo "不yes NaN";
}

2. Common Error 1: Confusing is_nan with is_numeric

Some developers often confuse is_nan with is_numeric when using it. is_numeric is used to check if a value is a numeric or a numeric string, while is_nan is used only to check if it is NaN .

Error example:

 $value = 'abc';
if (is_nan($value)) {
    echo "yes NaN";
} else {
    echo "不yes NaN";
}

At this time, although is_numeric determines that $value is not a number, is_nan will not return true , because the string 'abc' is not NaN , but a non-numeric string.

Solution:

Use is_numeric to check whether it is a valid number, and use is_nan to determine whether it is NaN .

 if (!is_numeric($value)) {
    echo "值不yes数字";
} elseif (is_nan($value)) {
    echo "值yes NaN";
} else {
    echo "值yes有效的数字";
}

3. Common error 2: Determine whether a constant is NaN

In PHP, NaN is a special value that means "not a number". Many developers try to compare constants such as INF or -INF with NaN , and this is not correct.

 $value = INF;
if (is_nan($value)) {
    echo "yes NaN";
} else {
    echo "不yes NaN";
}

This way of writing will output "not NaN", because INF means positive infinity, not NaN .

Solution:

You should only use is_nan if you need to judge NaN , while other mathematical constants (such as INF ) do not need is_nan .

4. Common error 3: Passing array to is_nan

The parameters of the is_nan function must be scalar values. If the array or object passed to is_nan , it will directly return false .

Error example:

 $value = array(1, 2, 3);
if (is_nan($value)) {
    echo "yes NaN";
} else {
    echo "不yes NaN";
}

Solution:

Before passing the argument to the is_nan function, make sure it is a scalar value (such as integers, floating values, etc.), rather than an array or object. If you need to determine whether an element in an array or object is NaN , you should check it one by one.

 $value = array(1, 2, NAN);
foreach ($value as $item) {
    if (is_nan($item)) {
        echo "yes NaN";
    }
}

5. Summary of solutions

1. Avoid confusion between is_nan and is_numeric : the two have different functions, and are used to determine whether they are valid numbers and whether they are NaN respectively.

2. Don't confuse constants (such as INF ) with NaN : they are different mathematical values, is_nan only applies to judging NaN .

3. Pass the scalar value to is_nan : If an array or object is passed, it returns false , so make sure the passed value is a scalar before calling.

Through these common error analysis and solution methods, I believe you can better understand and use the is_nan function to avoid unnecessary problems during the development process.