如何结合static_assert与sizeof和stringify？ [英] How to combine static_assert with sizeof and stringify?

问题描述

内存使用在我的应用程序是相当关键。因此，我有具体的断言，在编译时检查内存大小，并给出一个static_assert如果大小不同于我们认为正确之前。

我已经定义了一个宏像这样：

  #define CHECKMEM（mytype，size）static_assert（（sizeof（objectType）== size）不正确的#mytype！）; 
  

这个宏可以很容易写成：

  CHECKMEM（Book，144）; 
 CHECKMEM（图书馆，80）; 
  

问题是当这个static_assert关闭时，可能很难找出什么新的size应该是（例如通过使用隐藏的编译器选项/ d1 reportAllClassLayout）。
如果我可以包括实际大小，那么会更加方便，因此代替：

p>

会显示

！ （预计144，大小为152）

我尝试这样写：

  #define CHECKMEM（mytype，size）static_assert（（sizeof（objectType）== size）），size incorrect for#mytype！ is#sizeof（mytype）））; 
  

但是你不能在函数调用上使用stringize

我也试过添加双字符串技巧，如下所示：

  #define STR1（x）#x 
 #define STR2（x）STR1（x）
 #define CHECKMEM（mytype，size）static_assert（sizeof（objectType）== size） #mytype！（预期为#size，大小为STR2（sizeof（mytype））））; 
  

但不是打印 size is 152 打印 size是sizeof（Book）。

有没有办法在static_assert中stringize结果sizeof？

解决方案

我将在函数模板上使用dispatching来执行检查：

  #include< cstddef> 
 
 template< typename ToCheck，std :: size_t ExpectedSize，std :: size_t RealSize = sizeof（ToCheck）> 
 void check_size（）{
 static_assert（ExpectedSize == RealSize，Size is off！）; 
} 
 
 struct foo 
 {
 char bla [16]; 
}; 
 
 int main（）
 {
 check_size< foo，8>（）; 
 return 0; 
} 
  

结果：

 在实例化'void check_size（）[with ToCheck = foo; long unsigned int ExpectedSize = 8ul; long unsigned int RealSize = 16ul]'：
 bla.cpp：15：22：从这里需要
 bla.cpp：5：1：error：static assertion failed：Size is off！ 
  

调试信息在回溯的模板参数中。

如果这真的更好，你必须决定，它还取决于编译器。它还允许您使用模板映射隐藏预期大小，总计到最大大小和其他奇异的东西。

Memory usage is quite critical in my application. Therefore I have specific asserts that check for the memory size at compile time and give a static_assert if the size is different from what we considered correct before.

I have defined a macro like this:

#define CHECKMEM(mytype, size) static_assert((sizeof(objectType) == size)), "Size incorrect for " #mytype "!");

This macro makes it very easy to write this:

CHECKMEM(Book,144);
CHECKMEM(Library,80);

The problem is that when this static_assert goes off, it might be quite difficult to find out what the new size should be (e.g. by using the hidden compiler option "/d1 reportAllClassLayout"). It would be much handier if I could include the actual size, so instead of:

Size incorrect for Book!

It would show

Size incorrect for Book! (expected 144, size is 152)

I tried writing something like this:

#define CHECKMEM(mytype, size) static_assert((sizeof(objectType) == size)), "Size incorrect for " #mytype "! (expected" #size ", size is " #sizeof(mytype) ")");

But you can't use the stringize (#) operator on a function call.

I also tried adding the double-stringize trick, like this:

#define STR1(x) #x 
#define STR2(x) STR1(x) 
#define CHECKMEM(mytype, size) static_assert((sizeof(objectType) == size)), "Size incorrect for " #mytype "! (expected" #size ", size is " STR2(sizeof(mytype)) ")");

But instead of printing size is 152 it prints size is sizeof(Book).

Is there a way to stringify the result of sizeof in a static_assert?

解决方案

I'd use dispatching on a function template to do the checking:

#include <cstddef>

template <typename ToCheck, std::size_t ExpectedSize, std::size_t RealSize = sizeof(ToCheck)>
void check_size() {
  static_assert(ExpectedSize == RealSize, "Size is off!");
}

struct foo
{
  char bla[16];
};

int main()
{
  check_size<foo, 8>();
  return 0;
}

Results in:

In instantiation of ‘void check_size() [with ToCheck = foo; long unsigned int ExpectedSize = 8ul; long unsigned int RealSize = 16ul]’:
bla.cpp:15:22:   required from here
bla.cpp:5:1: error: static assertion failed: Size is off!

The debugging information is in the template parameters of the back-trace.

If this is truly better, you will have to decide and it also depends on the compiler. It also enables you to hide the expected size with a template map, to sum up to a max size and other fancy things.

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