String input problem

First definition

char* name;
scanf("%s",name);

Although the compilation is correct , Running will crash

The second definition

char[20] name;
scanf("%s",name);

You can run it successfully

1. About why it collapsed
   reason ： The reason why the program crashed , Because scanf Will put the string in the memory pointed to by the pointer . But the first one doesn't initialize the pointer . The pointer just points at . Put the string in a wrong place , Of course the program crashed .
   resolvent ： Insert a line between two lines of code name = (char*)malloc(32*sizeof(char)) Just fine , that 32 You can change it at will , That's the number of characters you can store

2. About string definition
   such as ：
   char *s = “Hello world”
   That's ok ,
   Because the program will put all the string constants to be used into Static memory in . then s Point to the address of the static memory with this string .
   But because it's static memory , So the content is Cannot be modified Of . If you want a string that can be modified , Then only char s[5] Or use malloc Allocate dynamic memory
   After initializing with string , The position pointed to by the pointer is read-only , You write data into it , The operating system is not allowed .

3. About scanf()
   Respective separators ：
   %s： Space 、 enter 、TAB key
   %d： Space 、 enter 、TAB key
   %c： There is no separator , The above delimiters are treated as normal characters
   in other words ： If it is %s%d, The delimiter encountered when reading data will be skipped until the first non empty input is encountered , Then you can not deal with it ’\n’.

4. About scanf(%s) and gets()
   char string[15];
   gets(string); / When a carriage return is encountered, the input is finished /
   scanf("%s",string); / When a space is encountered, it is considered that the input ends /
   String will be followed by ’\0’
   **scanf ：** When there is a carriage return , Space and tab The key will automatically add ’\0’, But enter , Space and tab The key remains in the input buffer .
   **gets：** All characters entered before the Enter key are acceptable , And use ’\0’ replace ‘\n’. Enter does not stay in the input buffer

For details, please refer to the following article ：
https://tieba.baidu.com/p/5079969028