BOOST_STATIC_ASSERT沒有提升

Question

因爲在我工作的公司中禁止提升，所以我需要在純C++中實現它的功能。我已經研究過助推源，但他們似乎太複雜，至少對我來說是無法理解的。我知道在C++ 0x standart中有一個叫static_assert()的東西，但我不想使用任何C++ 0x功能。

Answer 1

template<bool> struct StaticAssert; 
template<> struct StaticAssert<true> {}; 

int main() { 
    StaticAssert< (4>3) >(); //OK 
    StaticAssert< (2+2==5) >(); //ERROR 
} 

Answer 2

你可以從Boost source file宏簡單地複製到自己的代碼。如果您不需要支持Boost支持的所有編譯器，您可以爲編譯器選擇正確的定義，並省略該文件中其餘的#ifdef。

Answer 3

其他一招（其可以在C中使用的）是試圖建立一個數組具有負的大小，如果斷言失敗：

#define ASSERT(cond) int foo[(cond) ? 1 : -1] 

作爲獎勵，你可以使用一個typedef，而不是一個對象，因此，它在多個環境可用，並沒有發生，當它成功：

#define ASSERT(cond) typedef int foo[(cond) ? 1 : -1] 

最後，建立一個名稱與名稱衝突的機會更少（和可重複使用至少在不同線路）：

#define CAT_(a, b) a ## b 
#define CAT(a, b) CAT_(a, b) 
#define ASSERT(cond) typedef int CAT(AsSeRt, __LINE__)[(cond) ? 1 : -1] 

Answer 4

我使用下面的頭文件，用代碼從別人撕開......

#ifndef STATIC_ASSERT__H 
#define STATIC_ASSERT__H 

/* ripped from http://www.pixelbeat.org/programming/gcc/static_assert.html */ 

#define ASSERT_CONCAT_(a, b) a##b 
#define ASSERT_CONCAT(a, b) ASSERT_CONCAT_(a, b) 
/* These can't be used after statements in c89. */ 
#ifdef __COUNTER__ 
    /* microsoft */ 
    #define STATIC_ASSERT(e) enum { ASSERT_CONCAT(static_assert_, __COUNTER__) = 1/(!!(e)) } 
#else 
    /* This can't be used twice on the same line so ensure if using in headers 
    * that the headers are not included twice (by wrapping in #ifndef...#endif) 
    * Note it doesn't cause an issue when used on same line of separate modules 
    * compiled with gcc -combine -fwhole-program. */ 
    #define STATIC_ASSERT(e) enum { ASSERT_CONCAT(assert_line_, __LINE__) = 1/(!!(e)) } 
#endif 

/* http://msdn.microsoft.com/en-us/library/ms679289(VS.85).aspx */ 
#ifndef C_ASSERT 
#define C_ASSERT(e) STATIC_ASSERT(e) 
#endif 

#endif 

Answer 5

這是我自己實現從我的代碼庫中提取靜態斷言的：Pre-C++11 Static Assertions Without Boost。

用法：

STATIC_ASSERT(expression, message);

當靜態斷言測試失敗，則生成以某種方式包含STATIC_ASSERTION_FAILED_AT_LINE_xxx_message一個編譯器的錯誤消息。

message必須是一個有效的C++標識符，如no_you_cant_have_a_pony這將產生含有編譯器錯誤：

STATIC_ASSERTION_FAILED_AT_LINE_1337_no_you_cant_have_a_pony :)

#define CONCATENATE(arg1, arg2) CONCATENATE1(arg1, arg2) 
#define CONCATENATE1(arg1, arg2) CONCATENATE2(arg1, arg2) 
#define CONCATENATE2(arg1, arg2) arg1##arg2 

/** 
* Usage: 
* 
* <code>STATIC_ASSERT(expression, message)</code> 
* 
* When the static assertion test fails, a compiler error message that somehow 
* contains the "STATIC_ASSERTION_FAILED_AT_LINE_xxx_message" is generated. 
* 
* /!\ message has to be a valid C++ identifier, that is to say it must not 
* contain space characters, cannot start with a digit, etc. 
* 
* STATIC_ASSERT(true, this_message_will_never_be_displayed); 
*/ 

#define STATIC_ASSERT(expression, message)\ 
    struct CONCATENATE(__static_assertion_at_line_, __LINE__)\ 
    {\ 
    implementation::StaticAssertion<static_cast<bool>((expression))> CONCATENATE(CONCATENATE(CONCATENATE(STATIC_ASSERTION_FAILED_AT_LINE_, __LINE__), _), message);\ 
    };\ 
    typedef implementation::StaticAssertionTest<sizeof(CONCATENATE(__static_assertion_at_line_, __LINE__))> CONCATENATE(__static_assertion_test_at_line_, __LINE__) 

    // note that we wrap the non existing type inside a struct to avoid warning 
    // messages about unused variables when static assertions are used at function 
    // scope 
    // the use of sizeof makes sure the assertion error is not ignored by SFINAE 

namespace implementation { 

    template <bool> 
    struct StaticAssertion; 

    template <> 
    struct StaticAssertion<true> 
    { 
    }; // StaticAssertion<true> 

    template<int i> 
    struct StaticAssertionTest 
    { 
    }; // StaticAssertionTest<int> 

} // namespace implementation 


STATIC_ASSERT(true, ok); 
STATIC_ASSERT(false, ko); 

int main() 
{ 
    return 0; 
} 

Answer 6

我認爲這應該工作：

template<bool> struct CompileTimeAssert; 
template<> struct CompileTimeAssert<true>{}; 
#define STATIC_ASSERT(e) (CompileTimeAssert <(e) != 0>())