PHP中传值赋值和引用赋值的区别是什么?
PHP中传值赋值和引用赋值的区别是:1、传值赋值在函数范围内,改变变量值的大小,都不会影响到函数外边的变量值;2、引用赋值在函数范围内,对值的任何改变,在函数外部也有所体现,因为引用赋值赋的是内存地址。
传值赋值
传值赋值是将变量的值复制出一份新的值(值是一样的),只是在内存中出现两份不同的内存空间。将新值内存空间地址赋值给新的变量名字。修改两个变量的值时还不影响。
例如:将$a变量的值复制出一份存放到$b变量中.
因为他们各自指向自己的内存区域.
引用赋值
引用赋值是将变量的引用复制出来一份(新的引用还是指向原来的值)。
语法:
将$a变量引用复制出一份作为$b变量的引用. 两个变量的引用指向同一个内存空间.
通过&符号表示在赋值过程值使用引用赋值.
修改$a,$b的值都是修改值空间. 会相互影响两个变量的值.
PHP中传值赋值和引用赋值的区别(传值和传引用的区别)
php传值:在函数范围内,改变变量值的大小,都不会影响到函数外边的变量值。
PHP传引用:在函数范围内,对值的任何改变,在函数外部也有所体现,因为传引用传的是内存地址。
传值:和copy是一样的。打个比方,我有一橦房子,我给你建筑材料,你建了一个根我的房子一模一样的房子,你在你的房子做什么事都不会影响到我,我在我的房子里做什么事也不会影响到你,彼此独立。
<?php $testa=1; //定义变量a $testb=2; //定义变量b $testb = $testa; //变量a赋值给变量b echo $testb; //显示为1 ?>
传引用:类似于C语言的指针了,感觉差不多。打个比方,我有一橦房子,我给你一把钥匙,我们二个都可以进入这个房子,你在房子做什么都会影响到我。
<?php $param2=1; //定义变量2 $param1 = &$param2; //将变量2的引用传给变量1 echo $param2; //显示为1 $param1 = 2; //把2赋值给变量1 echo $param2; //显示为2 ?>
【优缺点:】传值会很耗时间,特别是对于大型的字符串和对象来说,这将会是一个代价很大的操作,传送引用,函数内的任何操作等同于对传送变量的操作,传送大型变量时效率高!
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