Description of string

There are often some short sentences in our daily life , We are C These short sentences are called strings in the language , But in C There is no string type in the language , So we use character arrays to generalize a string .

First , Let's introduce A character array The concept of

We will 'a','b','c','0' Data types enclosed in single quotation marks are called character types , For a string, it is composed of one character, so for a string , There should be a group like generalizing a large character type to define it , We call it a character array . How to use it is as follows

char a1[] = "abcdefg";// ad locum abcdef For a string 


char a2[] = {'a','b','c','d','e','f','g'};// ad locum abcdef Also a string 

In the previous code, we will use the string abcdef Stored in a character array , The writing form of character array is very similar to that of character type , That is, in the character type char Add a [ ], Here we can call it Character array type .

The above is a rough understanding of the string

Here we should have more questions and thoughts , Such as , What is the difference between the two forms of writing in the above code ？

Before making this clear, we need to understand array types carefully , See the link below ：

About arrays - Basics _m0_59725109 The blog of -CSDN Blog

• Let's introduce a function - strlen
• strlen It's a library function , Included in <string.h> in , Only used to calculate the number of characters in a string , Be careful ： Is only applicable to strings  , It works by counting back from the first element of the string , Until I find '\0'

We use stlen To calculate the number of characters in the above two writing methods

    char a1[] = "abcdefg";// ad locum abcdef For a string 


	char a2[] = { 'a','b','c','d','e','f','g' };// ad locum abcdef Also a string 

	printf("a1 = %d\n", strlen(a1));
	printf("a2 = %d\n", strlen(a2));

Get the results ：

  We find that in these two forms of writing strlen Calculation The number of characters is inconsistent , adopt strlen We can infer that These two strings are '\0' The location is different

Here are the results of debugging the code monitoring window ：

  It's not hard to find arrays a1 And array a2 The difference between the elements of a1 Than a2 One more. '\0' Elements , And it appears at the end of the array , We got strlen Compute string a1,a2 The reasons for the different results a1 Look back at the first element of the string '\0', Until I find '\0', remove '\0' After a total of 7 Elements , The result is 7, Because of the string a2 nothing '\0', therefore strlen Will always look back , Until I find '\0' until , So the result is random .

• We can also pass sizeof To test the results

    char a1[] = "abcdefg";// ad locum abcdef For a string 


	char a2[] = { 'a','b','c','d','e','f','g' };// ad locum abcdef Also a string 

	printf("a1 = %d\n", sizeof(a1));
	printf("a2 = %d\n", sizeof(a2));

sizeof The size of the data is calculated , A character type is 1 Bytes , And the array mentioned above a1 Ratio array a2 One more '\0'  combination , Array a1, Array a2 The size of should be 8,7

The code runs as follows ：