[C language] relevant distinction between strlen and sizeof

Blog home page ：Luo-Kuang- What

motto ： On the way to the peak of life together

Learning progress ：【C Language 】

Blog statement ： I will try my best to , Write every blog carefully , Let more friends exchange learning experiences with me .

If there is any deficiency , Please correct me. . Learning is the process of constantly making mistakes and correcting ！

Preface ：

We often need to know the length of some arrays to calculate or find a value , Usually I use strlen Functions and sizeof To get the results we want .

Define the distinction between ：

    1. First , Let me start with strlen And sizeof The difference between definitions

strlen It's a library function （ need #include<stdlib.h> The header file ）

strlen Is to find the length of the string , Whether there is... In the string of interest \0, Statistics \0 The number of characters that appear before

sizeof It's the operator

sizeof Only pay attention to how much memory space is occupied , Don't pay attention to the data stored in memory

---

Code display ：

     1. First show some related code

​

   2. Running results

​

---

Problem description ：

  I can see , The result may not be the same as we expected .

 1. The first is also strlen, but 2 Array initialization methods are different , The results are also different .

 2. The same is sizeof,2 The results of array initialization methods are also different , also arr1 It produced an unexpected number 15.

      2. arr1 And arr2 The difference between

char arr1[] = "abc";                     by ： a b c \0  

char arr2[] = { 'a', 'b', 'c' };          by ：  a b c    

    3. There are different reasons

First ：arr1 Initialize to string , And the string should use \0 ending , therefore arr1 The string will be automatically supplemented with \0

           arr2 Initialize to the specified 3 Characters , Unwanted \0 ending , It won't make up \0

---

Result analysis ：

1. Yes strlen The results were analyzed differently

  according to strlen Definition , Statistics \0 The number of characters before .

  therefore arr1 The result is 3

  because arr2 Not in it \0, According to the memory relationship , Will go to arr2 Open up the memory and look for \0, Until I find \0, Statistics \0 The number of characters before , It will be a random value , This time for 15

2. Yes sizeof The results were analyzed differently

  according to sizeof Definition , Count the number of bytes in the array （sizeof The unit of return value is bytes ）

  arr1 Array \0 It's also a character , And there are bytes , To be counted . therefore arr1 by 4 Byte space

  arr2 There is no \0, And only 3 Character station 3 Byte space

---

summary

 1. Array initialization （ In undetermined space size ） The string will be automatically added \0 End with

      For multiple characters , I won't add \0 ending

 2.strlen To statistics \0 The number of characters before （ It doesn't contain \0, And must find \0） Can only be used to find the length of a string

    sizeof Only count the number of bytes contained in the space of the array （ contain \0, because \0 It's also a character , Station one byte ）          String length -1 Give a matrix （ In especial int Type an array of single numbers ） All available

---

Conclusion ：

Dear friends , If you think it's useful, just give it to Bo Sanlian ！ If there is a mistake , Please correct me. , Thank you. ！ If you have different opinions , Please communicate with me , Progress together

We met at the summit ！！！️