Don't use array_push() inside a loop body-PHP Tutorial-php.cn

Don't use array_push() inside a loop body

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Release： 2023-04-07 18:14:02

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The title is don’t use array_push() in the loop body. In fact, this is just one of the conclusions of this article

Let’s study the appending elements of the array in the PHP language

Append elements to the array

We know that there are two ways for PHP to append elements to the end of the array stack

$a = []; array_push($a,'test');
$a[] = 'test';

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So what is the difference between these two methods?

Let’s compare the performance first

ArrayPush
一个 ArrayPush 类
pushEachOne() 循环体中使用 array_push() 来为 $a 追加元素
pushEachTwo() 循环体中使用 $a[] = $var 来为 $a 追加元素
/**
 * Class ArrayPush
 */
class ArrayPush
{
    /**
     * @param int $times
     * @return array
     */
    public static function pushEachOne(int $times): array
    {
        $a = [];
        $b = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
        for ($i = 0; $i < $times; $i++) {
            array_push($a, $b[$i % 10]);
        }
        return $a;
    }
    /**
     * @param int $times
     * @return array
     */
    public static function pushEachTwo(int $times): array
    {
        $a = [];
        $b = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
        for ($i = 0; $i < $times; $i++) {
            $a[] = $b[$i % 10];
        }
        return $a;
    }
}

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Write code test

Loop to append 1 million elements

ini_set('memory_limit', '4000M');
$timeOne = microtime(true);
$a       = ArrayPush::pushEachOne(1000000);
echo 'count pushEachOne result | ' . count($a) . PHP_EOL;
$timeTwo = microtime(true);
$b       = ArrayPush::pushEachTwo(1000000);
echo 'count pushEachTwo result | ' . count($b) . PHP_EOL;
$timeThree = microtime(true);
echo PHP_EOL;
echo 'pushEachOne | ' . ($timeTwo - $timeOne) . PHP_EOL;
echo 'pushEachTwo | ' . ($timeThree - $timeTwo) . PHP_EOL;
echo PHP_EOL;

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Result

The result is self-evident, $a[] = is nearly three times faster than using array_push()

count pushEachOne result | 1000000
count pushEachTwo result | 1000000
pushEachOne | 1.757071018219
pushEachTwo | 0.67165303230286

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Analysis

array_push () Why is it slow? It's so slow, are there any scenarios where we can use it?

Official Manual

array_push — 将一个或多个单元压入数组的末尾（入栈）
array_push ( array &$array , mixed $value1 [, mixed $... ] ) : int
array_push() 将 array 当成一个栈，并将传入的变量压入 array 的末尾。array 的长度将根据入栈变量的数目增加。和如下效果相同：

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And repeat the above actions for each incoming value.

● Note: If you use array_push() to add a unit to the array, it is better to use \$array[] = because there is no additional burden of calling the function.

● Note: array_push() will issue a warning if the first argument is not an array. This is different from the behavior of \$var[], which creates a new array.

Official source code

Look at array_push() in the source code

/* {{{ proto int array_push(array stack, mixed var [, mixed ...])
   Pushes elements onto the end of the array */
PHP_FUNCTION(array_push)
{
    zval   *args,       /* Function arguments array */
           *stack,      /* Input array */
            new_var;    /* Variable to be pushed */
    int i,              /* Loop counter */
        argc;           /* Number of function arguments */
    //这一段是函数的参数解析
    ZEND_PARSE_PARAMETERS_START(2, -1)
        Z_PARAM_ARRAY_EX(stack, 0, 1)
        Z_PARAM_VARIADIC('+', args, argc)
    ZEND_PARSE_PARAMETERS_END();
    /* For each subsequent argument, make it a reference, increase refcount, and add it to the end of the array */
    for (i = 0; i < argc; i++) {
        //拷贝一个
        ZVAL_COPY(&new_var, &args[i]);
        //插入新数值，自动
        if (zend_hash_next_index_insert(Z_ARRVAL_P(stack), &new_var) == NULL) {
            if (Z_REFCOUNTED(new_var)) Z_DELREF(new_var);
            php_error_docref(NULL, E_WARNING, "Cannot add element to the array as the next element is already occupied");
            RETURN_FALSE;
        }
    }
    /* Clean up and return the number of values in the stack */
    RETVAL_LONG(zend_hash_num_elements(Z_ARRVAL_P(stack)));
}
/* }}} */

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$a[] = The implementation is called according to the assigned variable type A series of Zend_API functions add_next_index_*, which directly call zend_hash_next_index_insert after setting a zval value of the corresponding type

ZEND_API int add_next_index_long(zval *arg, zend_long n) /* {{{ */
{
    zval tmp;
    ZVAL_LONG(&tmp, n);
    return zend_hash_next_index_insert(Z_ARRVAL_P(arg), &tmp) ? SUCCESS : FAILURE;
}
/* }}} */
ZEND_API int add_next_index_null(zval *arg) /* {{{ */
{
    zval tmp;
    ZVAL_NULL(&tmp);
    return zend_hash_next_index_insert(Z_ARRVAL_P(arg), &tmp) ? SUCCESS : FAILURE;
}
/* }}} */
ZEND_API int add_next_index_bool(zval *arg, int b) /* {{{ */
{
    zval tmp;
    ZVAL_BOOL(&tmp, b);
    return zend_hash_next_index_insert(Z_ARRVAL_P(arg), &tmp) ? SUCCESS : FAILURE;
}
/* }}} */
ZEND_API int add_next_index_resource(zval *arg, zend_resource *r) /* {{{ */
{
    zval tmp;
    ZVAL_RES(&tmp, r);
    return zend_hash_next_index_insert(Z_ARRVAL_P(arg), &tmp) ? SUCCESS : FAILURE;
}
/* }}} */
ZEND_API int add_next_index_double(zval *arg, double d) /* {{{ */
{
    zval tmp;
    ZVAL_DOUBLE(&tmp, d);
    return zend_hash_next_index_insert(Z_ARRVAL_P(arg), &tmp) ? SUCCESS : FAILURE;
}
/* }}} */
ZEND_API int add_next_index_str(zval *arg, zend_string *str) /* {{{ */
{
    zval tmp;
    ZVAL_STR(&tmp, str);
    return zend_hash_next_index_insert(Z_ARRVAL_P(arg), &tmp) ? SUCCESS : FAILURE;
}
/* }}} */
ZEND_API int add_next_index_string(zval *arg, const char *str) /* {{{ */
{
    zval tmp;
    ZVAL_STRING(&tmp, str);
    return zend_hash_next_index_insert(Z_ARRVAL_P(arg), &tmp) ? SUCCESS : FAILURE;
}
/* }}} */
ZEND_API int add_next_index_stringl(zval *arg, const char *str, size_t length) /* {{{ */
{
    zval tmp;
    ZVAL_STRINGL(&tmp, str, length);
    return zend_hash_next_index_insert(Z_ARRVAL_P(arg), &tmp) ? SUCCESS : FAILURE;
}
/* }}} */
ZEND_API int add_next_index_zval(zval *arg, zval *value) /* {{{ */
{
    return zend_hash_next_index_insert(Z_ARRVAL_P(arg), value) ? SUCCESS : FAILURE;
}
/* }}} */

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Summary

After the above analysis, it seems that array_push() It has no meaning of existence, is it really so?

● Generally, the performance of array_push() is too poor, so we should use $array[] = to replace it

● If you append multiple units at a time, use array_push()

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