Question

Do you know of a function that can check if a string contains an integer?

Here’s how I’d expect it to work:

holds_int("23") // should return true.  
holds_int("2.3") // should return false.  
holds_int("qwe") // should return false.

Answer 1

if((string)(int)$var == $var) {
    echo 'var is an integer or a string representation of an integer';
}

Example results:

var_dump( test(1)             ); // TRUE
var_dump( test('1')           ); // TRUE
var_dump( test('1.0')         ); // TRUE
var_dump( test('1.1')         ); // false
var_dump( test('0xFF')        ); // false
var_dump( test('0123')        ); // TRUE
var_dump( test('01090')       ); // TRUE
var_dump( test('-1000000')    ); // TRUE
var_dump( test('+1000000')    ); // TRUE
var_dump( test('2147483648')  ); // false
var_dump( test('-2147483649') ); // false

See Gordon’s answer below for how this would behave differently if === were used for comparison instead of ==.