is_string() of an integer or float returns false, so it might be useful to include an is_numeric() when checking if a value is stringy:
function is_stringy($val) {
return (is_string($val) || is_numeric($val)
|| (is_object($val) && method_exists($val, '__toString')));
}
?>
Test code (which should print "vector N OK" for each test vector):
foreach ([[NULL, false], [false, false], [true, false],
[0, true], [[], false], [0.1, true], ["x", true],
["", true], [new Exception("x"), true]] as $idx => $vector) {
list ($val, $expected) = $vector;
if (is_stringy($val) != $expected) {
print ("mismatch at $idx\n");
var_dump($val);
} else {
print ("vector $idx OK\n");
}
}
?>
The following is an example of how to test if a variable is set, whether or not it is NULL. It makes use of the fact that an unset variable will throw an E_NOTICE error, but one initialized as NULL will not.
function var_exists($var){
if (empty($GLOBALS['var_exists_err'])) {
return true;
} else {
unset($GLOBALS['var_exists_err']);
return false;
}
}
function var_existsHandler($errno, $errstr, $errfile, $errline) {
$GLOBALS['var_exists_err'] = true;
}
$l = NULL;
set_error_handler("var_existsHandler", E_NOTICE);
echo (var_exists($l)) ? "True " : "False ";
echo (var_exists($k)) ? "True " : "False ";
restore_error_handler();
?>
Outputs:
True False
The problem is, the set_error_handler and restore_error_handler calls can not be inside the function, which means you need 2 extra lines of code every time you are testing. And if you have any E_NOTICE errors caused by other code between the set_error_handler and restore_error_handler they will not be dealt with properly. One solution:
function var_exists($var){
if (empty($GLOBALS['var_exists_err'])) {
return true;
} else {
unset($GLOBALS['var_exists_err']);
return false;
}
}
function var_existsHandler($errno, $errstr, $errfile, $errline) {
$filearr = file($errfile);
if (strpos($filearr[$errline-1], 'var_exists') !== false) {
$GLOBALS['var_exists_err'] = true;
return true;
} else {
return false;
}
}
$l = NULL;
set_error_handler("var_existsHandler", E_NOTICE);
echo (var_exists($l)) ? "True " : "False ";
echo (var_exists($k)) ? "True " : "False ";
is_null($j);
restore_error_handler();
?>
function var_exists($var){
if (empty($GLOBALS['var_exists_err'])) {
return true;
} else {
unset($GLOBALS['var_exists_err']);
return false;
}
}1
function var_exists($var){
if (empty($GLOBALS['var_exists_err'])) {
return true;
} else {
unset($GLOBALS['var_exists_err']);
return false;
}
}2
In summary, strcmp() does not necessarily use the ASCII code order of each character like in the 'C' locale, but instead parse each string to match language-specific character entities (such as 'ch' in Spanish, or 'dz' in Czech), whose collation order is then compared. When both character entities have the same collation order (such as 'ss' and '?' in German), they are compared relative to their code by strcmp(), or considered equal by strcasecmp().
The LC_COLLATE locale setting is then considered: only if LC_COLLATE=C or LC_ALL=C does strcmp() compare strings by character code.
Generally, most locales define the following order:
control, space, punctuation and underscore, digit, alpha (lower then upper with Latin scripts; or final, middle, then isolated, initial with Arabic script), symbols, others...
With strcasecmp(), the alpha subclass is ignored and consider all forms of letters as equal.
Note also that some locales behave differently with accented characters: some consider they are the same letter as the unaccented letter (with a minor collation order, e.g. French, Italian, Spanish), some consider they are distinct letters with an independant collation order (e.g. in the C locale, or in Nordic languages).
Finally, the collation string is not considering individual characters but instead groups of characters that form a single letter:
- for example "ch" or "CH" in Spanish which is always after all other strings beginning with 'c' or 'C', including "cz", but before 'd' or 'D';
- 'ss' and '?' in German;
- 'dz', 'DZ' and 'Dz' in some Central European languages written with the Latin script...
- UTF-8, UTF-16 (Unicode), S-JIS, Big5, ISO2022 character encoding of a locale (the suffix in the locale name) first decode the characters into the UCS4/ISO10646 code position before applying the rules of the language indicated by the main locale...
So be extremely careful to what you consider a "character", as it may just mean a encoding byte with no significance in the string collation algorithm: the first character of the string "cholera" in Spanish is "ch", not "c" !
Can you use == to compare strings in PHP?
The assignment operator assigns the variable on the left to have a new value as the variable on right, while the equal operator == tests for equality and returns true or false as per the comparison results. Example: This example describes the string comparison using the == operator.
How to compare to string in PHP?
The strcmp() function compares two strings. Note: The strcmp() function is binary-safe and case-sensitive. Tip: This function is similar to the strncmp() function, with the difference that you can specify the number of characters from each string to be used in the comparison with strncmp().
How do you check if a variable is a string?
To check if a variable contains a value that is a string, use the isinstance built-in function. The isinstance function takes two arguments. The first is your variable. The second is the type you want to check for.
How to compare to variable in PHP?
Identical Operator ===
The comparison operator called as the Identical operator is the triple equal sign “===”. This operator allows for a much stricter comparison between the given variables or values. This operator returns true if both variable contains same information and same data types otherwise return false.
