C language pointer initialization and assignment

1. pointer Initialization

At first glance, it seems that the initialization and assignment of pointers are very confusing, and *, and an array is generated from time to time. In fact, the summary is very simple:

Int * P;

Int A = 25;

Int B [10];

Int * m = &;

Int * n = B;

Int * r = & B [0];

The pointer definition is as shown above. A variable with the * Header represents this variable as a pointer variable.

During pointer initialization, the right operand of "=" must be the address of the data in the memory. It cannot be a variable or an integer address value (but int * p = 0; except, this statement indicates that the pointer is null ). In this case, * P only indicates that a pointer variable is defined and has no indirect value.

Int * s = 15;

Int * s = {2, 3, 5 };

Int * s =;

The above three initialization methods are all incorrect.

2. pointer assignment

P = m;

P = &;

P = B;

* P = 25;

* P =;

* P = B [4];

Pointer assignment. The left operand of "=" can be * P or P.

When the left operand of "=" is * P, it changes the data stored by the address pointed to by P. When the left operand of "=" is P, the address pointed to by P is changed.

The array variable name B indicates the first address of the array, so P = B; is also correct.

3. "Special Circumstances"

As mentioned above, the variable address must be used for pointer initialization, rather than directly using the variable.

So how can we explain the following:

Char * CP = "ABCD ";

In fact, this initialization process points the pointer CP to the first address of the string, rather than passing the string value. Because, in C language, there is no overall processing mechanism for a string.

Therefore, we add a quotation mark to the title "special case", because it is actually a pointer initialized with the variable address, and "special case" is not special.

As a result, how to assign values to pointers using strings? The following method is used:

CP = "mnop ";

Statements such as * CP = "mnop" are incorrect. The reason is that the String constant transmits its first address.

In addition, this initialization process has another implicit meaning: "ABCD" is a String constant, and no string replication occurs during the initialization process, instead, it simply points the pointer to the String constant. Therefore, you cannot use * CP to modify the value of the string because the string is a constant. Of course, we can use "cp =" to modify the string to which the Pointer Points. the pointer itself is not a constant.

If you try to modify the string through the * CP pointer, what will happen? The answer is undefined, depending on the compiler. At least one thing is certain. In the compilation phase, the compiler will not report an error because * CP is not a constant, so assigning a value to * CP has no syntax error. However, some compilers, such as Vc, will throw an exception at runtime: an access conflict occurs when the write location is 0x00415768 (the address pointed by CP!

This is different from charca [] = "ABCD". The data in the string can be modified through Ca [X.