C中的2D数组如何成为1D数组？ [英] How do 2D arrays in C become 1D arrays?

问题描述

如果有人可以向我解释以下行为，我将非常感激：

说我声明一个静态2D数组

  float buffer [NX] [NY]; 
  

现在，如果我想填充这个数组，我注意到可以这样做：

  initarray（buffer，NX，NY）; 
 
 #define INITDATAVAL 0.5 
 
 void initarray（void * ptr，int nx，int ny）
 {
 int i，j; 
 
 float * data =（float *）ptr; 
 
 for（i = 0; i  {
 data [i] = INITDATAVAL;我的问题是，如果buffer是一个二维数组，那么我们可以使用一个数组，一旦传递到 initarray 函数，它如何用作一维数组？我很难理解... 
 
 
 
当2D数组被静态分配时，分配的内存是连续的，但是如果 
解决方案
具有3 x 4个元素的2D数组）在内存中如下：
  A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4 
  
由于底层存储是连续的，可以简单地将数组转换为指向第一个元素的指针，并使用单个偏移（ buffer 传递给 initarray ）。 
 
 
 
（在此示例中，编译器会将 buffer [n] [m]  code> buffer + n * NY + m 基本上，二维数组只是存储在一维数组中的二维数据的一个舒适的符号）。
 
I would appreciate if someone could explain to me the following behavior:

Say I declare a static  2D array
float buffer[NX][NY];
Now, if I want to populate this array, I have notice that it could be done this way:
initarray(buffer, NX, NY);

#define INITDATAVAL 0.5

void initarray(void *ptr, int nx, int ny)
{
  int i, j;

  float *data = (float *) ptr;

  for (i=0; i < nx*ny; i++)
    {
      data[i] = INITDATAVAL;
    }
}
My question is, if buffer is a 2D array, how can it be used as a 1D array once it is passed to initarray function? I am struggling to understand it...

When 2D arrays are statically allocated, the memory allocated is contiguous, but could this way be used if buffer is dynamically allocated instead?
解决方案
A 2D array with 3 x 4 elements (i.e. a matrix) looks like this in memory:
A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4
Since the underlying storage is continuous, one can simply convert the array to a pointer to the first element and access all elements using a single offset (this 'cast', which is called 'decaying' in such a context, happens automatically when buffer is passed to initarray). 

(In this sample, the compiler would translate an expression such as buffer[n][m] to buffer + n*NY+m Basically, 2D arrays are just a comfortable notation for 2D data stored in 1D arrays).

                        
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