Question

我正在整理一些使用“幻数”的旧代码来设置硬件寄存器，我想使用常量代替这些数字来使代码更具表现力（实际上它们会映射到用于记录寄存器的名称/值。）

然而，我担心随着变化的数量，我可能会打破神奇的数字。这是一个简化的例子（寄存器集更复杂）：

const short mode0 = 0;
const short mode1 = 1;
const short mode2 = 2;

const short state0 = 0;
const short state1 = 4;
const short state2 = 8;

所以代替：

set_register(5);

我们有：

set_register(state1|mode1);

我正在寻找的是构建时间版本：

ASSERT(5==(state1|mode1));

更新

@Christian，感谢快速响应，我对C / non-boost环境的答案感兴趣，因为这是驱动程序/内核代码。

Answer 1

新答案：

在我的原始答案（下面）中，我必须有两个不同的宏来支持函数作用域和全局作用域中的断言。我想知道是否有可能提出一个适用于两个范围的解决方案。

我能够找到一个适用于使用外部字符数组的Visual Studio和Comeau编译器的解决方案。但我能够找到适用于GCC的更复杂的解决方案。但GCC的解决方案不适用于Visual Studio。 :(但是添加一个'#ifdef __ GNUC __'，很容易为给定的编译器选择正确的宏集。

<强>解决方案：

#ifdef __GNUC__
#define STATIC_ASSERT_HELPER(expr, msg) \
    (!!sizeof \ (struct { unsigned int STATIC_ASSERTION__##msg: (expr) ? 1 : -1; }))
#define STATIC_ASSERT(expr, msg) \
    extern int (*assert_function__(void)) [STATIC_ASSERT_HELPER(expr, msg)]
#else
    #define STATIC_ASSERT(expr, msg)   \
    extern char STATIC_ASSERTION__##msg[1]; \
    extern char STATIC_ASSERTION__##msg[(expr)?1:2]
#endif /* #ifdef __GNUC__ */

以下是在test.c第22行报告的STATIC_ASSERT(1==1, test_message);错误消息：

<强> GCC

line 22: error: negative width in bit-field `STATIC_ASSERTION__test_message'

Visual Studio：

test.c(22) : error C2369: 'STATIC_ASSERTION__test_message' : redefinition; different subscripts
    test.c(22) : see declaration of 'STATIC_ASSERTION__test_message'

<强>科莫：

line 22: error: declaration is incompatible with
        "char STATIC_ASSERTION__test_message[1]" (declared at line 22)

原始回答：

我做的事与Checkers的做法非常相似。但是我在很多编译器中都会显示一条消息：

#define STATIC_ASSERT(expr, msg)               \
{                                              \
    char STATIC_ASSERTION__##msg[(expr)?1:-1]; \
    (void)STATIC_ASSERTION__##msg[0];          \
}

要在全局范围内（在函数外部）执行某些操作，请使用：

#define GLOBAL_STATIC_ASSERT(expr, msg)   \
  extern char STATIC_ASSERTION__##msg[1]; \
  extern char STATIC_ASSERTION__##msg[(expr)?1:2]

Answer 2

有一篇文章 Ralf Holly检查C中静态断言的不同选项。

他提出了三种不同的方法：

切换案例值必须是唯一的
数组不得包含负尺寸
为常量表达式除以零

他对最佳实施的结论如下：

#define assert_static(e) \
    do { \
        enum { assert_static__ = 1/(e) }; \
    } while (0)

Answer 3

Checkout boost static assert

Answer 4

如果您无法访问第三方库静态断言函数（如boost），则可以滚动自己的静态断言：

#define STATIC_ASSERT(x) \
    do { \
        const static char dummy[(x)?1:-1] = {0};\
    } while(0)

当然，缺点是错误消息不会非常有用，但至少它会为您提供行号。

Answer 5

#define static_assert(expr) \
int __static_assert(int static_assert_failed[(expr)?1:-1])

它可以在任何地方，任何时间使用。我认为这是最简单的解决方案。

使用前，请仔细使用您的编译器进行测试。

Answer 6

尝试：

#define STATIC_ASSERT(x, error) \
do { \
    static const char error[(x)?1:-1];\
} while(0)

然后你可以写：

STATIC_ASSERT(a == b, a_not_equal_to_b);

这可能会为您提供更好的错误消息（取决于您的编译器）。

Answer 7

此处列出的任何技术均可使用，当C ++ 0x可用时，您将可以使用内置的static_assert关键字。

Answer 8

如果你有Boost，那么使用BOOST_STATIC_ASSERT是可行的方法。如果你正在使用C或者不想获得Boost 这是我的c_assert.h文件，用于定义（并解释）一些用于处理静态断言的宏的工作方式。

它应该是更复杂的因为在ANSI C代码中你需要2个不同的宏 - 一个可以在你有声明的区域工作，一个可以在正常语句所在的区域工作。还有一些工作可以使宏在全局范围或块范围内工作，以及一堆gunk以确保没有名称冲突。

STATIC_ASSERT()可用于变量声明块或全局范围。

STATIC_ASSERT_EX()可以是常规陈述。

对于C ++代码（或允许声明与语句混合的C99代码）STATIC_ASSERT()可以在任何地方使用。

/*
    Define macros to allow compile-time assertions.

    If the expression is false, an error something like

        test.c(9) : error XXXXX: negative subscript

    will be issued (the exact error and its format is dependent
    on the compiler).

    The techique used for C is to declare an extern (which can be used in
    file or block scope) array with a size of 1 if the expr is TRUE and
    a size of -1 if the expr is false (which will result in a compiler error).
    A counter or line number is appended to the name to help make it unique.  
    Note that this is not a foolproof technique, but compilers are
    supposed to accept multiple identical extern declarations anyway.

    This technique doesn't work in all cases for C++ because extern declarations
    are not permitted inside classes.  To get a CPP_ASSERT(), there is an 
    implementation of something similar to Boost's BOOST_STATIC_ASSERT().  Boost's
    approach uses template specialization; when expr evaluates to 1, a typedef
    for the type 

        ::interslice::StaticAssert_test< sizeof( ::interslice::StaticAssert_failed<true>) >

    which boils down to 

        ::interslice::StaticAssert_test< 1>

    which boils down to 

        struct StaticAssert_test

    is declared. If expr is 0, the compiler will be unable to find a specialization for

        ::interslice::StaticAssert_failed<false>.

    STATIC_ASSERT() or C_ASSERT should work in either C or C++ code  (and they do the same thing)

    CPP_ASSERT is defined only for C++ code.

    Since declarations can only occur at file scope or at the start of a block in 
    standard C, the C_ASSERT() or STATIC_ASSERT() macros will only work there.  For situations
    where you want to perform compile-time asserts elsewhere, use C_ASSERT_EX() or
    STATIC_ASSERT_X() which wrap an enum declaration inside it's own block.

 */

#ifndef C_ASSERT_H_3803b949_b422_4377_8713_ce606f29d546
#define C_ASSERT_H_3803b949_b422_4377_8713_ce606f29d546

/* first some utility macros to paste a line number or counter to the end of an identifier
 * this will let us have some chance of generating names that are unique
 * there may be problems if a static assert ends up on the same line number in different headers
 * to avoid that problem in C++ use namespaces
*/

#if !defined( PASTE)
#define PASTE2( x, y) x##y
#define PASTE( x, y)  PASTE2( x, y)
#endif /* PASTE */

#if !defined( PASTE_LINE)
#define PASTE_LINE( x)    PASTE( x, __LINE__)
#endif /* PASTE_LINE */

#if!defined( PASTE_COUNTER)
#if (_MSC_VER >= 1300)      /* __COUNTER__ introduced in VS 7 (VS.NET 2002) */
    #define PASTE_COUNTER( x) PASTE( x, __COUNTER__)   /* __COUNTER__ is a an _MSC_VER >= 1300 non-Ansi extension */
#else
    #define PASTE_COUNTER( x) PASTE( x, __LINE__)      /* since there's no __COUNTER__ use __LINE__ as a more or less reasonable substitute */
#endif
#endif /* PASTE_COUNTER */



#if __cplusplus
extern "C++" {   // required in case we're included inside an extern "C" block
    namespace interslice {
        template<bool b> struct StaticAssert_failed;
        template<>       struct StaticAssert_failed<true> { enum {val = 1 }; };
        template<int x>  struct StaticAssert_test { };
    }
}
    #define CPP_ASSERT( expr) typedef ::interslice::StaticAssert_test< sizeof( ::interslice::StaticAssert_failed< (bool) (expr) >) >  PASTE_COUNTER( IntersliceStaticAssertType_)
    #define STATIC_ASSERT( expr)    CPP_ASSERT( expr)
    #define STATIC_ASSERT_EX( expr) CPP_ASSERT( expr)
#else
    #define C_ASSERT_STORAGE_CLASS extern                  /* change to typedef might be needed for some compilers? */
    #define C_ASSERT_GUID 4964f7ac50fa4661a1377e4c17509495 /* used to make sure our extern name doesn't collide with something else */
    #define STATIC_ASSERT( expr)   C_ASSERT_STORAGE_CLASS char PASTE( PASTE( c_assert_, C_ASSERT_GUID), [(expr) ? 1 : -1])
    #define STATIC_ASSERT_EX(expr) do { enum { c_assert__ = 1/((expr) ? 1 : 0) }; } while (0)
#endif /* __cplusplus */

#if !defined( C_ASSERT)  /* C_ASSERT() might be defined by winnt.h */
#define C_ASSERT( expr)    STATIC_ASSERT( expr)
#endif /* !defined( C_ASSERT) */
#define C_ASSERT_EX( expr) STATIC_ASSERT_EX( expr)



#ifdef TEST_IMPLEMENTATION
C_ASSERT( 1 < 2);
C_ASSERT( 1 < 2);

int main( )
{
    C_ASSERT( 1 < 2);
    C_ASSERT( 1 < 2);

    int x;

    x = 1 + 4;

    C_ASSERT_EX( 1 < 2);
    C_ASSERT_EX( 1 < 2);



    return( 0);
}
#endif /* TEST_IMPLEMENTATION */
#endif /* C_ASSERT_H_3803b949_b422_4377_8713_ce606f29d546 */

Answer 9

常见的便携式选项是

#if 5 != (state1|mode1)
#    error "aaugh!"
#endif

但在这种情况下它不起作用，因为它们是C常量而不是#define s。

您可以看到Linux内核的BUILD_BUG_ON宏用于处理您案例的内容：

#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))

当condition为真时，这变为((void)sizeof(char[-1]))，这是非法的，应该在编译时失败，否则变为((void)sizeof(char[1]))，这很好。

Answer 10

确保使用足够新的编译器进行编译（例如gcc -std=c11）。

然后你的陈述就是：

_Static_assert(state1|mode1 == 5, "Unexpected change of bitflags");

Answer 11

 old= array([[  65, 108, 105,  32, 105, 115,  32, 116, 104, 101,  32,66,101,
       115, 116,  32, 105, 110,  32, 116, 104, 101,  32, 119, 111, 114,
       108, 100,  32, 121, 101, 101, 104, 104, 104, 104, 104, 104, 104,
       104, ..., 170, 170, 170],
       [171, 171, 171, ..., 170, 170, 170],
       [171, 171, 171, ..., 170, 170, 170],
       ...,
       [ 17,  17,  17, ...,  17,  17,  17],
       [ 17,  17,  17, ...,  17,  17,  17],
       [ 17,  17,  17, ...,  17,  17,  17]], dtype=uint8)

这不像单行MY_ASSERT（expr）解决方案那样优雅。在编译C代码之前，可以使用sed，awk或m4宏处理器来生成MY_ASSERT（expr）的DEBUG代码扩展为多行或NODEBUG代码以将其删除以进行生产。

在C语言中在构建时ASSERT表达式的方法

11 个答案: