兼容类型和结构用C [英] Compatible types and structures in C

问题描述

我有以下的code：

  INT主要（无效）
{
    结构{INT X; } A，B;
    结构{INT X; } C;
    结构{INT X; } * P;    B = A; /* 好 */
    C = A; / *不*工作/
    P =＆放大器;一个; / *不*工作/    返回0;
}
 

而失败GCC（3.4.6）下进行编译，并出现以下错误：

  test.c以8：错误：不兼容的类型赋值
test.c的：9：警告：分配从兼容的指针类型
 

现在，从我的理解（当然从C99标准），是 A 和 C 应兼容类型，因为他们履行6.2.7节的所有标准，第1款。我试着 STD = C99 编译，都无济于事。

presumably标准间我pretation是错的？

附录

顺便说一句，这个问题是因为我想声明一些类似模板的宏来包装各种数据类型，而无需到处申报命名的类型/类型定义，例如开销一个简单的例子：

 的#define LINKED_LIST（T）\\
    结构{\\
        T * PHEAD; \\
        T * PTAIL; \\
    }...LINKED_LIST（富）list1的;
LINKED_LIST（富）列表2;...LINKED_LIST（富）* PLIST =安培; list1的; / *不*工作/
 

解决方案

综观的 我猜你是依靠语句后随之而来条件的规定草案：

  

此外，二元结构，联合或枚举在不同的翻译单位申报类型是兼容的，如果他们的标签和成员符合下列要求...

我认为，事实上，这些都是在同一个C文件decared意味着他们是在一个单一的翻译单元。

在猜测它似乎，这保证了当两个C文件包含一个声明类型的标题则该类型的实例将是兼容的。

I have the following code:

int main(void)
{
    struct { int x; } a, b;
    struct { int x; } c;
    struct { int x; } *p;

    b = a;   /* OK */
    c = a;   /* Doesn't work */
    p = &a;  /* Doesn't work */

    return 0;
}

which fails to compile under GCC (3.4.6), with the following error:

test.c:8: error: incompatible types in assignment
test.c:9: warning: assignment from incompatible pointer type

Now, from what I understand (admittedly from the C99 standard), is that a and c should be compatible types, as they fulfill all the criteria in section 6.2.7, paragraph 1. I've tried compiling with std=c99, to no avail.

Presumably my interpretation of the standard is wrong?

Addendum

Incidentally, this question arises because I wanted to declare some template-like macros to wrap various datatypes without the overhead of having to declare named types/typedefs everywhere, e.g. a trivial example:

#define LINKED_LIST(T)   \
    struct {             \
        T    *pHead;     \
        T    *pTail;     \
    }

...

LINKED_LIST(foo) list1;
LINKED_LIST(foo) list2;

...

LINKED_LIST(foo) *pList = &list1;  /* Doesn't work */

解决方案

Looking at the draft specification I'm guessing you're relying on the conditions that come after the statement:

Moreover, two structure, union, or enumerated types declared in separate translation units are compatible if their tags and members satisfy the following requirements ...

I think that the fact that these are all decared in the same C file means that they are in a single translation unit.

At a guess it would seem that this guarantees that when two C files include a header that declares a type then instances of that type will be compatible.

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