Summary of two-dimensional array parameter passing in C Language

Recently, I am working on matrix operations. Based on previous lazy ideas, I want to directly create a function that can transmit a matrix of any dimension for calculation.
 
Therefore, the void matrix_mult (float ** p) function is declared );
 
Then, the main function declares a two-dimensional array float a [3] [3];
 
In this case, matrix_mult ();
 
Then, the compiler prompts: cannot convert parameter 1 from 'float [3] [3] 'to 'float **'
 
There is an error.
 
Correction Method:
 
Matrix_mult (float (* p) [N]); // N declares the second-dimensional size value of the two-dimensional array, and then transmits the parameter matrix_mult (a); OK.
 
 
Summary: this is a common question: array and pointer
 
Note:
 
A pointer is a variable name, while an array is not a variable name. An array is similar to a struct.
 
Example:
 
Int * p; int a [2]; p =;
Int n = sizeof (p );//
 
Int len = sizeof ();
 
The value of n is 4, and the value of len is 8;
 
 
Int a [10] [20]; // a real two-dimensional array,
 
Int * B [10]; // The definition is assigned with 10 pointers without initialization. In other words, B is a pointer array composed of 10 INTEGER (int) pointers.
 
Int (* p) [3]; // pointer to an array
 
Int (* p) (); // pointer to the Function
 
Int * p (); // p is a function, and the returned value is an int pointer.
 
 
Float ** here p is not a pointer to a two-dimensional array, but a pointer to a pointer, that is, a second-level pointer.
The correct pointer to a two-dimensional array should be: Int a [2] [2]; Int (* p) [2]; // when defining the array dimension, only the first dimension can be ignored.
 
 
 
A two-dimensional array is actually a pointer, while a second-level pointer is a pointer to a pointer, so the two are not equivalent.
 
 
 
Appendix: code
 
/*----------------------------------------------------------------------------------*/
 
/* Description: this function can be used to multiply the Matrix 3x3 directly. It has been verified */
 
/*----------------------------------------------------------------------------------*/
 
# Include "stdlib. h"
# Include "stdio. h"
# Include "math. h"
 
 
Void matrix_mult (float (* a) [3], float (* B) [3], float (* c) [3]);
Void matrix_init (float (* a) [3]);
 
 
 
 
Float a [3] [3] = {1, 2, 3, 4, 5, 6, 7, 8, 9 };
Float B [3] [3] = {2, 3, 4, 5, 6, 7, 8, 9, 1 };
Float c [3] [3] = {0 };
 
 
 
Int main ()
{
Int I, j;
 
 
Int t [2];
Int * p;
P = t;
 
 
Int n = sizeof (p );
Int len = sizeof (t );
 
 
Printf ("the original array C value is \ n ");
For (I = 0; I <3; I ++)
{
For (j = 0; j <3; j ++)
{
Printf ("% f", c [I] [j]);
}
Printf ("\ n ");
}
Printf ("\ n ");
 
 
Printf ("the value of original array A is \ n ");
For (I = 0; I <3; I ++)
{
For (j = 0; j <3; j ++)
{
Printf ("% f", a [I] [j]);
}
Printf ("\ n ");
}
Printf ("\ n ");
 
 
Printf ("the original array B value is \ n ");
For (I = 0; I <3; I ++)
{
For (j = 0; j <3; j ++)
{
Printf ("% f", B [I] [j]);
}
Printf ("\ n ");
}
Printf ("\ n ");
 
// Initialize data
Matrix_init (c); // matrix_init (* c) [3]);
 
 
// Matrix_init (* c) [3]);
Printf ("the C value of the initialization array is \ n ");
For (I = 0; I <3; I ++)
{
For (j = 0; j <3; j ++)
{
Printf ("% f", c [I] [j]);
}
Printf ("\ n ");
}
Printf ("\ n ");
 
Matrix_mult (a, B, c); // matrix_mult (float (* a) [3], float (* B) [3], float (* c) [3])
// Matrix_mult (* a) [3], (* B) [3], (* c) [3]);
Printf ("the value of array C after multiplication is \ n ");
For (I = 0; I <3; I ++)
{
For (j = 0; j <3; j ++)
{
Printf ("% f", c [I] [j]);
}
Printf ("\ n ");
}
Printf ("\ n ");
 
 
Return 0;
 
}
 
 
Void matrix_mult (float (* a) [3], float (* B) [3], float (* c) [3])
{
Int I, j, k;
 
For (I = 0; I <3; I ++)
{
For (j = 0; j <3; j ++)
{
For (k = 0; k <3; k ++)
{
C [I] [j] + = a [I] [k] * B [k] [j];
}
}
}
 
}
 
 
 
 
Void matrix_init (float (* a) [3])
{
Int I = 3;
Int j = 3; www.2cto.com
 
For (I = 2; I> = 0; I --)
{
For (j = 2; j> = 0; j --)
{
A [I] [j] = 0;
}
}
}