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This article mainly introduces "the concept of C language string". In daily operation, I believe that many people have doubts about the concept of C language string. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubts about the concept of C language string! Next, please follow the editor to study!

Catalogue

Case description

Case analysis

Necessary knowledge

1, character array

(1) definition of character array

(2) initialization of character array

2, string concept

(1) the concept of string

(2) initialize the character array with characters

(3) get the length of the string

3, string and pointer

4, character array and character pointer

Case description

String substitution is one of the most common operations when dealing with strings, and it is also the knowledge that must be mastered when learning strings. This case requires programmatic conversion of the string "Good moring" to "Good evening".

Case analysis

We need to start where the string is replaced and copy the content to be replaced into the original string one by one until the end of the string or the end of the replaced string.

In order to successfully complete the case, we need to learn the basics of character array, string, character pointer and so on.

Necessary knowledge

1, character array

A character array is an array of character data, in which each element is a single character

(1) definition of character array

The syntax format of the character array definition is as follows:

Char array name [constant expression]; char array name [constant expression 1] [constant expression 2]

In the above syntax, the methods of defining one-dimensional character array and two-dimensional character array are listed respectively.

The sample code is as follows:

Char ch [6]; (2) initialization of character array

While the array is defined, you can also assign values to the elements in the array, a process called array initialization. The sample code is as follows:

Char c [5] = {'henceforth, thecontrol, thecontrol.

Be careful

Initializing an array of characters is simple, but note the following.

(1) the number of elements cannot be more than the size of the character array, otherwise the compiler will make an error.

(2) if the initial item is less than the length of the array, the remaining elements are assigned to empty characters ('\ 0')

(3) if the array size is not specified, the compiler allocates the length of the array according to the number of initial items.

(4) you can also initialize two-dimensional arrays

(basically the same as the integer array)

2, string concept

(1) the concept of string

A string is a string of characters made up of numbers, letters, underscores, spaces, and so on. It is a constant, with a'\ 0' as the Terminator at the end of the string by default.

"abcde"

"

The above two lines are strings, except that the characters in the second string are spaces

Strings are very important data types in various programming languages, but there is no fixed type of strings in C language. Strings are usually stored and processed in the form of an array of characters, which must end with'\ 0'. When you put a string in a character array, you should also put the Terminator in the array, so the length of the character array is the actual number of characters plus one.

(2) initialize the character array with characters

To facilitate initialization of a character array, you can directly use a string constant to assign a value to another character array, as shown in the following example:

Char char_array [6] = {"hello"}; char char_array [] = {"hello"}; (3) get the length of the string

Strings are stored in arrays, sizeof operators are used to calculate the length of various data types, and sizeof operators can also be used to calculate the length of strings, such as sizeof ("abcde").

In addition to using the sizeof operator, you can also use the strlen () function to get the string length, as shown in the prototype of the strlen () function:

Unsigned int strlen (char * s)

Where s is the pointer to the string and the return value is the length of the string. It is important to note that the string obtained using the strlen () function does not include the empty character'\ 0' at the end.

The sizeof operator and the strlen () function are different in finding strings.

The differences between the two are as follows:

1Magnesizeof is the operator, and the strlen () function is a C language standard library function, contained in the stringh header file.

2the function of the strlen sizeof operator is to get the byte size of the created object and to calculate the memory occupied by the type; the () function is to get the effective number of bytes occupied by the string.

3The arguments to the strlen sizeof operator can be arrays, pointers, types, objects, functions, etc. The arguments to the () function must be pointers to a string ending in'\ 0'.

4the size calculation of the strlen sizeof operator is completed at compile time, so it cannot be used to calculate the size of dynamically allocated memory; the result of the memory () function can only be calculated at run time.

Be careful

A string in C is actually an array of characters, and characters are a basic data type, and it is easy to convert between characters and strings. Next, convert char a ='A'to a string, as follows:

(1) create a character array of length 2:

Char a_str [2]

(2) set the first element to the corresponding character and the second element to the empty character.

A_str [0] = a * str [1] ='\ 0'

Similarly, it is easy to convert a string to multiple characters, as shown in the following example:

Char a_str [] = "AB"; char a = a_atr [0]; char b = a_atr [1]

In the above code, a character array a_str [] is defined, in which the string "AB" is saved. As long as each character of the string is assigned to the character variable aperior b, the string can be converted to a character.

3, string and pointer

In C language, character pointer is defined by char *, which can point not only to a character constant, but also to a string. To describe the relationship between a string and a pointer, the sample code is as follows:

Char char_array [] = "hello"; char* ch = char_array

In the above code, the character pointer ch points to both the character'h' and the string "hello": if outputted with "% c", only the characters pointed to by the current pointer are output; if outputted with "% s", the data of subsequent consecutive memory space is output until'\ 0' is encountered.

4, character array and character pointer

Character arrays and character pointers, you can also take array addresses and assign values to character pointers. The character array and the character pointer are inextricably linked around the string, so let's summarize the difference and relationship between the two:

(1) Storage method

When a character array is initialized with a string, the string is stored in the memory space opened up by the character array; when the character pointer variable is initialized with a string constant, the first address of the string is stored in the pointer variable. but the string is stored in the constant area.

The above text is rather obscure. Here is a sample code to help you understand it, as follows:

Char str [6] = "hello"; char*p = "hello"

The variables defined in the above two lines of code are stored in the memory area as shown in the figure:

(2) initialization and assignment method

Initialization mode

You can assign values to character pointer variables, but not to array names. The sample code is as follows:

Char * p = "hello"; / / equivalent to char * p; p = "hello"; char str [6] = "hello"; / / char atr [6]; str = "hello"; this is an error

Assignment method

Strings defined by an array can only be assigned by assigning values to the elements in the array one by one or by calling the assignment function, while strings defined by pointers can also be assigned directly. The sample code is as follows:

Char * p1 = "hello", * p2; p1 = p2witchar str1 [6] = "hello", str2 [6]; / / str1 = str2 error, array assignment is not feasible

(3) character pointer and array name

The character pointer variable can be changed, and the array name is a pointer constant whose value cannot be changed. the code example is as follows:

Char * p = "hello world"; p + = 7; / / character pointer variable can be changed

For the character array char str [6] = "hello", the array name is a constant pointer and cannot be changed

(4) references to characters in a string

You can use the subscript method and the address method to refer to the array elements. similarly, you can also use the address method and pointer variable subscript method to reference the character elements of the string. The example code is as follows:

Char * p str [100] = "hello world"; char ch2 = str [6]; char * p = "hello world"; char ch3 = p [6]; / / equivalent to char ch3 = * (p + 6) at this point, the study of "C language string concept" is over, hoping to solve everyone's doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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