你总是可以加零！

Input             Output
'2' + 0           2 (int)
'2.34' + 0        2.34 (float)
'0.3454545' + 0   0.3454545 (float)

如果你事先不知道你有一个浮点数还是一个整数，如果字符串可能包含特殊字符（如空格、欧元等），并且如果它可以包含多于1个点或逗号，您可以使用此功能：

// This function strip spaces and other characters from a string and return a number.
// It works for integer and float.
// It expect decimal delimiter to be either a '.' or ','
// Note: everything after an eventual 2nd decimal delimiter will be removed.
function stringToNumber($string) {
    // return 0 if the string contains no number at all or is not a string:
    if (!is_string($string) || !preg_match('/\d/', $string)) {
        return 0;
    } 

    // Replace all ',' with '.':
    $workingString = str_replace(',', '.', $string);

    // Keep only number and '.':
    $workingString = preg_replace("/[^0-9.]+/", "", $workingString);

    // Split the integer part and the decimal part,
    // (and eventually a third part if there are more 
    //     than 1 decimal delimiter in the string):
    $explodedString = explode('.', $workingString, 3);

    if ($explodedString[0] === '') {
        // No number was present before the first decimal delimiter, 
        // so we assume it was meant to be a 0:
        $explodedString[0] = '0';
    } 

    if (sizeof($explodedString) === 1) {
        // No decimal delimiter was present in the string,
        // create a string representing an integer:
        $workingString = $explodedString[0];
    } else {
        // A decimal delimiter was present,
        // create a string representing a float:
        $workingString = $explodedString[0] . '.' .  $explodedString[1];
    }

    // Create a number from this now non-ambiguous string:
    $number = $workingString * 1;

    return $number;
}

你总是可以加零！

Input             Output
'2' + 0           2 (int)
'2.34' + 0        2.34 (float)
'0.3454545' + 0   0.3454545 (float)

使用一元运算符（+）。例如：

$n1 = +'7';
$n2 = '2.34';
$n2 = +$n1;

var_dump（$n1）：int（7）var_dump（$n2）：浮点（2.34）

仅将数字乘以1，以便将字符串转换为类型number。

//String value
$string = "5.1"
if(is_numeric($string)){
  $numeric_string = $string*1;
}

派对迟到了，但这里有另一种方法：

function cast_to_number($input) {
    if(is_float($input) || is_int($input)) {
        return $input;
    }
    if(!is_string($input)) {
        return false;
    }
    if(preg_match('/^-?\d+$/', $input)) {
        return intval($input);
    }
    if(preg_match('/^-?\d+\.\d+$/', $input)) {
        return floatval($input);
    }
    return false;
}

cast_to_number('123.45');       // (float) 123.45
cast_to_number('-123.45');      // (float) -123.45
cast_to_number('123');          // (int) 123
cast_to_number('-123');         // (int) -123
cast_to_number('foo 123 bar');  // false