C language (i) scanf (), scanf_s () and error C4996

Fatal error C4996

Beginner C, the first I/O function to touch is scanf (). However, when compiling code in a later version of Visual Studio (including but not limited to 2015, 2013, 2012), unexpected errors occur.
Here's a simple code:

 #include  " stdio.h  "  int  Main (void   int   I; printf (  " input i\n  "  ); scanf (  " %d      ", &i); printf (  " i is%d  "  , I);  return  0  ;}  

But it will output an error C4996, the error message is as follows

Error 1 C4996: ' scanf ': This function or variable could be unsafe. Consider using scanf_s instead. To disable deprecation, use _crt_secure_no_warnings. See online Help for details.

Error said scanf unsafe, recommended to replace scanf scanf_s. After the replacement, the code is as follows

 #include  " stdio.h  "  int  Main (void   int   I; printf (  " input i\n  "  ); scanf_s (  " %d      ", &i); printf (  " i is%d  "  , I);  return  0  ;}  

There are no error hints.

scanf and scanf_s

In MSDN there are functions that end with _s, including scanf_s, scanf_s_l, wscanf_s, and _wscanf_s_l. These versions of the functions have security enhancements.

scanf functions exist in the older CRT (C Runtime Library, part of the C library) and have security issues, such as when reading a character, without specifying the width of%s, can cause a buffer overflow.

When using scanf, if the read width is specified, no error will be made. Modify the code as follows:

 #include  " stdio.h  "  int  Main (void   int   I; printf (  " input i\n  "  ); scanf_s (  " %5d      ", &i); printf (  " i is%d  "  , I);  return  0  ;}  

This controls the read-in%d width of 5. However, when the data read exceeds the width limit, data is lost. For example, this is input 100000, the output I value is 10000.

Workaround

1. Specify the width when using scanf.

2. Replace the sacnf with sacnf_s.

3. Cancel the SDL check at the time of the new project.

C language (i) scanf (), scanf_s () and error C4996