GCC 2.9＆QUOT;左值要求作为分配及QUOT的左操作数;

问题描述

我一直空指针玩弄创造这个例子：

I have been playing around with void pointers and created this example:

#include <stdio.h>

struct intint {
    int a;
    int b;
};

struct intshortshort {
    int a;
    short b;
    short c;
};

void fill_me(struct intint **pii, void *piss)
{
    (void*)*pii = piss;                // Question about this line?
}

int main()
{
    struct intint *pii = NULL;
    struct intshortshort iss;
    iss.a = iss.b = iss.c = 13;

    fill_me(&pii, &iss);

    printf("%d..%d\n", pii->a, pii->b);


    return 0;
}

问：

当我使用gcc版本2.95.4一切编译和按预期工作，但gcc版本4.7.3给了我以下错误：

When I'm using gcc version 2.95.4 everything compiles and works as expected, but gcc version 4.7.3 gives me following error:

void_pointer.c:16:17: error: lvalue required as left operand of assignment

时有一个原因增加（无效*），以左值不再被允许的？

Is there a reason why adding (void *) to lvalue is not allowed anymore?

编辑：谢谢您的回答，我想我明白这个问题，但问题的为什么？这是摆在首位OK仍是有趣的

Thank you for answers, I think I understood the problem, but the question "why it was ok in the first place?" is still interesting.

推荐答案

这问题不是关于无效* ，大约是类型转换和左值。

This question isn't about the void*, is about typecast and lvalue.

例如：

#include <stdio.h>

int main()
{
    int n;
    (int)n = 100;
    return 0;
}

这code会引起同样的错误：如需要转让的左操作数左值

this code will causes same error: lvalue required as left operand of assignment.

这是因为 = 运营商需要修改的左值作为其左操作数。

That because the = operator requires a modifiable-lvalue as its left operand.

那么，什么是左值？又有什么修改的左值？请参阅

So, what is the lvalue? and what's the modifiable-lvalue? Please see wikipedia:Value.

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