Pointer essence analysis

Pointer essence analysis

1. Variables Review: variable in the program is but another name for a storage space, it is not necessary to use this storage space by the alias?
2. Another variable may be changed by the pointer
3. The nature of pointers to variables (as long as the variables, there is an address), but say that this variable is special, it is stored in the variable address value
4. When pointer declaration, * represents the declared variable number of pointers
5. When using the pointer, the pointer value takes asterisk indicates points to memory space
6. * Similar to a key number, the memory can be opened by the key, read the value in memory
7. Different pointers, memory occupied by the same. All 32-bit system, the pointer bytes are occupied 4

Call-by-call and pass-by

1. A pointer is a variable, you can declare a pointer parameter
2. When the internal body of a function to change the value of the argument, it is necessary to use a pointer parameter
3. Function call, the argument value is copied to the parameter
4. Pointer function parameters for complex data types

Constant pointer

. 1  const  int * p;              // p variable content of non-variable p at 
2  int  const * p;              // p variable, the content pointed to by p immutable 
. 3  int * const p;             // p immutable, p points the contents of the variable 
. 4  const  int * const p;       // p and p points are not variable content

Formulas: from the left and right finger , when const * number appears when the pointer to the left of the data is constant , when const appears to the right of the pointer itself is constant asterisk

 1 #include <stdio.h>
 2 int main()
 3 {
 4      int i = 0;
 5      const int *p1 = &i;
 6      int const *p2 = &i;
 7      int* const p3 = &i;
 8      const int * const p4 = &i;
 9      p1  = NULL; //ok
10      *p1 = 1;    //error
11      p2 = NULL;  //ok
12      *p2 = 1;    //error
13      p3 = NULL;  //error
14      *p3 = 1;    //ok
15      p4 = NULL;  //error
16      *p4 = 1;    //error
17      return 0;
18 }

operation result:

1> ------ Rebuild All started: Project: constants and pointers, configuration: Debug Win32 ------
1>  main.c
1> j: \ c language exercises \ constants and pointers \ constants and pointers \ main.c (15): error C2166 : left value specifies const Object
1> j: \ c language exercises \ constants and pointers \ constants and pointers \ main.c (18): error C2166 : left value specifies const Object
1> j: \ c language exercises \ constants and pointers \ constants and pointers \ main.c (20): error C2166 : left value specifies const Object 1> j: \ c language exercises \ constants and pointers \ constants and pointers \ main.c (23): error C2166 : left value specifies const Object 1> j: \ c language exercises \ constants and pointers \ constants and pointers \ main.c (24): error C2166 : left value specifies const object is ========== Rebuild All: Success 0 , a failure, 0 skipped ==========