str_starts_with

(PHP 8)

str_starts_with — Checks if a string starts with a given substring

说明

str_starts_with ( string $haystack , string $needle ) : bool

Performs a case-sensitive check indicating if haystack begins with needle.

参数

haystack

The string to search in.

needle

The substring to search for in the haystack.

返回值

Returns true if haystack begins with needle, false otherwise.

范例

Example #1 Using the empty string ''

<?php
if (str_starts_with('abc', '')) {
    echo "All strings start with the empty string";
}
?>

以上例程会输出：

All strings start with the empty string

Example #2 Showing case-sensitivity

<?php
$string = 'The lazy fox jumped over the fence';

if (str_starts_with($string, 'The')) {
    echo "The string starts with 'The'\n";
}

if (str_starts_with($string, 'the')) {
    echo 'The string starts with "the"';
} else {
    echo '"the" was not found because the case does not match';
}

?>

以上例程会输出：

The string starts with 'The'
"the" was not found because the case does not match

注释

Note: 此函数可安全用于二进制对象。

参见

  • str_contains() - Determine if a string contains a given substring
  • str_ends_with() - Checks if a string ends with a given substring
  • stripos() - 查找字符串首次出现的位置（不区分大小写）
  • strrpos() - 计算指定字符串在目标字符串中最后一次出现的位置
  • strripos() - 计算指定字符串在目标字符串中最后一次出现的位置（不区分大小写）
  • strstr() - 查找字符串的首次出现
  • strpbrk() - 在字符串中查找一组字符的任何一个字符
  • substr() - 返回字符串的子串
  • preg_match() - 执行匹配正则表达式

User Contributed Notes

jgusta 11-Mar-2021 10:14
With credit to Paul Phillips for the original polyfill posted.

If you do not have PHP 8, you can use these functions to get the capability of the new string functions.

But! Remember to use a conditional check to make sure the function is not already defined.

<?php
// source: Laravel Framework
// https://github.com/laravel/framework/blob/8.x/src/Illuminate/Support/Str.php
if (!function_exists('str_starts_with')) {
    function str_starts_with($haystack, $needle) {
        return (string)$needle !== '' && strncmp($haystack, $needle, strlen($needle)) === 0;
    }
}
if (!function_exists('str_ends_with')) {
    function str_ends_with($haystack, $needle) {
        return $needle !== '' && substr($haystack, -strlen($needle)) === (string)$needle;
    }
}
if (!function_exists('str_contains')) {
    function str_contains($haystack, $needle) {
        return $needle !== '' && mb_strpos($haystack, $needle) !== false;
    }
}
?>

This keeps it from breaking in case you upgrade and forget that you added it. This is a good practice generally when using the global scope for your helper functions.
Paul Phillips 22-Feb-2021 02:55
You can use this in PHP versions less than 8.

<?php
function str_starts_with ( $haystack, $needle ) {
  return strpos( $haystack , $needle ) === 0;
}