C中编译时的数组定义 [英] Array definition at compile time in C

问题描述

大家好

有人可以告诉我如何使用预处理器在编译时初始化数组。

以上是我认为的替代方案。我的实际问题如下：

  //  我有以下两种结构 
  typedef   struct  
 {
  float  rahul [ 6 ]; 
} RahulT; 
 
  typedef   struct  Max {
  int  ax; 
  const   float  * f1; 
  const   float  * f2; 
} tMax; 
 
  //  对结构进行初始化并声明指向它的指针。 
  const  RahulT RahulTvar = {{ 3 ， 4 ， 6 ， 8 ， 9 ， 7 }}; 
  const  RahulT * pRahulTvar =& RahulTvar; 
 
  //  在第二个静态const str中使用结构的数组。 
  static   const  tMax teststr = {
  11   / *   Nx：* / ，
&（pRahulTvar-> ; rahul [ 0 ]）， //  这是给予错误：错误C2099：初始化程序不是常数 
&（RahulTvar.rahul [ 0 ]） //  工作正常 
 
}; 

为什么会出现问题。什么是可能的解决方案。

我想使用指针选项来保存临时内存复制操作。但是在指针的情况下它会给出问题。

解决方案

错误消息有点明确：初始化程序不是常量 - 它不是。



就编译器而言，对象的地址不是常量值，因为它是由链接器定义的，它将程序及其数据定位在内存空间中。编译器没有 - 如果根据它的大小定义所有内容，并让链接器整理出实际地址。



但你不能使用的值在任何情况下任何变量都是常数值 - 这就是你要做的事情。

即使你这样做了：

 < span class =code-keyword> int  ii =  6 ; 
 静态  const  tMax teststr = {
 ii，
  0 ，
  0 }; 

你会得到同样的错误！

我不太明白为什么我的建议在C ++中有效，但在C中却没有。所以我检查了其他人是否遇到了同样的问题。事实上，我在SO上找到了一个条目，第二个响应提供了一个可理解的解释，以及可能对您的情况有所帮助的解决方法：



http://stackoverflow.com/questions/12217165/const-pointer-pointing-to-a-const -pointer [ ^ ]

Hi All
can anyone please tell me how to initialize an array at compile time using preprocessor.
Above is the aternative That I thought. My actual problem is as below:

//I have following two structure
typedef struct
{
 float rahul[6];
}RahulT;

typedef struct Max{					
   int ax;
   const float* f1;
   const float* f2;
} tMax;

//intitialze the structure and declare a pointer to it.
const RahulT  RahulTvar={{3,4,6,8,9,7}};
const RahulT*  pRahulTvar = &RahulTvar;

//using the structures's array in second static const str.
static const tMax teststr = {
   11 /* Nx:  */, 
  &(pRahulTvar->rahul[0]),//this is giving error:  error C2099: initializer is not a constant
  &(RahulTvar.rahul[0])// it is working properly
  
};

Why is the problem is there. and what is the possible solution.
I want to use pointer option to save temporary memory copy operation. But in case of pointer it is giving problem.

解决方案

The error message is kinda explicit: "initializer is not a constant" - which it isn't.

The address of an object is not a constant value as far as the compiler is concerned, because it is defined by the linker which locates the program and its data inside the memory space. The compiler doesn't - if defines everything in terms of it's size, and lets the linker sort out the actual address.

But you can't use the value of any variable as a constant value under any circumstances - which is what you are trying to do.
Even if you did this:

int ii = 6;
static const tMax teststr = {
    ii,
    0,
    0};

You would get the same error!

I couldn't quite understand why the suggestion I made works in C++, but not in C. So I checked to see if others came across the same problem. Indeed I found an entry on SO, and the second response offers a halfway understandable explanation as well as a workaround that might help in your situation:

http://stackoverflow.com/questions/12217165/const-pointer-pointing-to-a-const-pointer[^]

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