[C language - zero foundation lesson 13] the mystery of string

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This issue is about the mystery of string , If there is any mistake, please point out thank you ！

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Catalog

What is a string ？

In the string ’\0‘ 

Definition of string

Input and output of string

String input and output functions

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What is a string ？

In our impression, it seems to be Chinese characters and symbols . And in the C In language, values consist of numbers 、 Letter 、 A string of characters made up of underscores . Of course, I think there are our Chinese characters , Of course, Chinese characters also belong to Chinese strings . What do strings do ？ Integer and real are used to store integer and real variables , We can guess that string is used to store string variables . That's right , It's true . stay C The use of a single character in a language char Type to store , A type larger than one character cannot be used to store . So we use the array , Because arrays can store multiple data of the same type .

In the string ’\0‘ 

＇＼0＇ Is the identification that determines the end of the character array , Indicates that this string of characters has reached the end ; or ＇＼0＇ It's the end of a string , Any string is automatically followed by ＇＼0＇. And the characters don't ‘\0’, Only the string has, at the end of the string, we can't see . The computer will automatically add... After the string ’\0‘.

Definition of string

The array used to store character data is character array , An element in a string array holds a character .

char a[4];

Initialization of string

	char a[5]={'A','B','C','D','E'};
	char b[5]={'A','B'};
	char c[]={'A','B'};

  Be careful ： There is no after the character array \0 Of

Character arrays and strings

	char a[5]={"ABCD"};
	char b[5]="ABCD";
	char c[5]="ABCD!"
	char d[]="ABCD!"

result ：

A character array a The length of is 5 Only saved 4 The last element is a \0 One byte of

A character array b The length of is 5 Only saved 4 The last element is a \0 One byte of

A character array c The length of is 5 Save 5 The last element is not \0 Of

A character array d There is no defined length of, so there is also a... At the end \0 So d The length of is 6

ask char[] e=“helloworld”; This array e How many elements are there ？

Input and output of string

Strings can take advantage of scanf function and printf function

char a[5]="ABCD";
	printf("%c\n",a[1]);
    printf("%s",a);

  result ：

B

ABCD

%c Is to output a single character %s It's the output string

String input and output functions

String input function gets

String output function puts

	char a[20];
	gets(a);
	puts(a);

	char a[20]="abc";
	char b[20]="cba";
	puts(a);
	puts(b);

result :

abc
cba

Be careful ：puts and gets Only used for input and output of string .

There are always spaces in the string. You must use gets(),puts()

puts() Automatic line feed effect

gets() Auto wrap when carriage return symbol is encountered

String function

Strlen function

Strlen The function is a function of the length of the test string , barring ’\0’

printf("%d\n",strlen("abc"));
	printf("%d\n", strlen("ab\0c"));
	printf("%d\n", strlen("\t\t\077"));

result :

3
2
3

String copy function strcpy

form ：strcpy（ character string 1, character string 2）

Use ： The string 2 Copy to string 1 in

Be careful ： character string 1 The length of cannot be less than the string 2 The length of

char a[20] = "";
	char b[20] = "def";
	strcpy(a, b);
	puts(a);
	puts(b);

  result :

def

def

String concatenation function strcat

form ：strcat（ A character array 1, A character array 2）

Use ： Connect strings in two character arrays , Put the string 2 Received string 1 after

Be careful ： character string 1 The array must be large enough , To accommodate the characters after the link , String after connection 1 The back ‘\0‘ Cancel , Keep only the last ’\0‘

	char a[20] = "abc";
	char b[20] = "def";
	strcat(a, b);
	puts(a);
	puts(b);

  result :

abcdef
def

String comparison function strcmp

form ：strcmp（ character string 1, character string 2）

Use ： Compare strings 1 And string

Be careful ： When comparing two strings, compare them one by one from left to right according to Ascil Compare the size of the code

form	result
character string 1> character string 2	1
character string 1= character string 2	0
character string 1< character string 2	-1

  If there is only one, the comparison is completed once , If there are multiple, if the front is equal, compare the next one until it is the last one .

printf("%d\n",strcmp("abc","abc"));
	printf("%d\n", strcmp("abd", "abc"));
	printf("%d\n", strcmp("aba", "abc"));

  result :

0
1
-1

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