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PHP 全局变量_PHP教程

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Jul 13, 2016 am 10:34 AM

aspnet 軟體程式設計

<?<span php
</span><span $name</span> = "why"<span ;
</span><span function</span><span  changeName(){
    </span><span $name</span> = "what"<span ;
}<br />changeName();
</span><span echo</span> "my name is " . <span $name</span> . "<br/>"<span ;
</span>?>

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　　执行代码的结果是：my name is why，而不是执行changeName()后显示what。分析原因，这是因为函数体changeName内$name变量被缺省设置为局部变量,$name的作用域就是在changeName内。于是，修改代码，添加全局变量如下：

<?<span php
</span><span global</span> <span $name</span><span ;
</span><span $name</span> = "why"<span ;
</span><span function</span><span  changeName(){
    </span><span $name</span> = "what"<span ;
}<br />changeName();
</span><span echo</span> "my name is " . <span $name</span> . "<br/>"<span ;
</span>?>

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　　注意：

　　定义全局变量后执行的结果仍然为my name is why，这个结果让我吃惊。原来，" 也就是说，当一个函数引用一个外部变量时，可以在函数内通过global来声明该变量，这样该变量就可以在函数中使用了（相当于当作参数传递进来）。那么，再次修改代码：

<?<span php
</span><span $name</span> = "why"<span ;
</span><span function</span><span  changeName(){
    </span><span global</span> <span $name</span><span ;
    </span><span $name</span> = "what"<span ;
}
changeName();
</span><span echo</span> "my name is " . <span $name</span> . "<br/>"<span ;
</span>?>

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　　这次的运行结果是：my name is what，说明

<?<span php
</span><span $name</span> = "why"<span ;
</span><span function</span><span  changeName(){
    </span><span global</span> <span $name</span><span ;
    </span><span $name</span> = "what"<span ;
}
</span><span function</span><span  changeName2(){
    </span><span $name</span> = "where"<span ;
}
changeName();
changeName2();
</span><span echo</span> "my name is " . <span $name</span> . "<br/>"<span ;
</span>?>

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<?<span php
</span><span $name</span> = "why"<span ;
</span><span function</span><span  changeName(){
    </span><span $GLOBALS</span>['name'] = "what"<span ;
}
changeName();
</span><span echo</span> "my name is " . <span $name</span> . "<br/>"<span ;
</span>?>

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<?<span php
</span><span $var1</span> = 1<span ;
</span><span $var2</span> = 2<span ;
</span><span function</span><span  test1(){
    </span><span $GLOBALS</span>['var2'] = &<span $GLOBALS</span>['var1'<span ];
}
test1();
</span><span echo</span> <span $var2</span> . "<br />"<span ;

</span><span $var3</span> = 1<span ;
</span><span $var4</span> = 2<span ;
</span><span function</span><span  test2(){
    </span><span global</span> <span $var3</span>,<span $var4</span><span ;
    </span><span $var4</span> = &<span $var3</span><span ;
}
test2();
</span><span echo</span> <span $var4</span> . "<br />"<span ;
</span>?>

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　　; 就可以访问它们。与所有其他超全局变量不同，$GLOBALS在PHP中总是可用的。另一个例子：

<?<span php
</span><span $var1</span> = 1<span ;
</span><span function</span><span  test1(){
    </span><span unset</span>(<span $GLOBALS</span>['var1'<span ]);
}
test1();
</span><span echo</span> <span $var1</span> . "<br />"<span ;

</span><span $var2</span> = 1<span ;
</span><span function</span><span  test2(){
    </span><span global</span> <span $var2</span><span ;
    </span><span unset</span>(<span $var2</span><span );
}
test2();
</span><span echo</span> <span $var2</span><span ;
</span>?>

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