[C language] about scanf() and scanf_ Some problems of s()

About scanf() And scanf_s() Some of the problems

About scanf() The main defect of is that it can not limit the number of input characters , It is extremely easy to cause the problem of memory overflow , Cause the program to crash .
Let's take a look at an example :

 Environmental Science ：Visual Studio 2019

#include "stdio.h"
#include "stdlib.h"
#pragma warning(disable : 4996)

int main()
{
    
	char* str = (char*)malloc(sizeof(char) * 11);
	scanf("%s", str);
	printf("%s\n", str);

	return 0;
}

There is no problem with normal input , When we type more than 10 The following conditions will occur when the number of characters is ：

Here you can see that the return value is no longer 0 了 , Actually in str The inside of the address has exploded , It will directly lead to program errors .

About the solution , Microsoft provides scanf_s() Limit it , Its use method is ：

scanf_s("%s", str, 11);

This 11 This limits the reading of characters , At the same time, it will be right str Check the boundaries , Set the last byte as 0. It should be noted that ANSI C There is no scanf_s(), Only scanf(), It only applies to Microsoft Visual Studio.
Use this function to modify as follows ( At the same time, it avoids Visual Studio Of C4996 error ):

#include "stdio.h"
#include "stdlib.h"

int main()
{
    
	char* str = (char*)malloc(sizeof(char) * 11);
	scanf_s("%s", str, 11);

	return 0;
}

After execution, you can see that the return value is normal .

Be careful ：
There was a small problem in the middle of the trip , Use scanf_s() After that, it is not normal to cross the boundary printf 了 , Before 2017 It's still normal , do not know why 2019 This is a problem , Wait till you're free .