参考资料：
- The GNU C Standard Library Reference Manual: https://www.gnu.org/software/libc/manual/pdf/libc.pdf
- C Language Reference at cppreference.com https://en.cppreference.com/w/c
- C Standard Library Headers at cppreference.com https://en.cppreference.com/w/c/header
- Microsoft’s C Language Reference: https://docs.microsoft.com/en-us/cpp/c-language/c-language- reference
1、输入输出类
标准输入输出类（控制台IO）<stdio.h>
- printf
- scanf
- scanf_s
- getchar
- putchar
- puts
gets（不建议使用）
文件输入输出类 <stdio.h>
- fopen
- fclose
- fread
- fwrite
- fgets
- fputs
- fscanf
- fprintf
- fseek
- ftell
- rewind
- feof
- ferror
- clearerr
低级输入输出类（POSIX系统）<unistd.h>
- read
- write
- open
- close
2、字符串转换数值类
字符串转换为整数 <stdlib.h>
- atoi
- strtol
- strtoul
- strtoull
字符串转换为浮点数 <stdlib.h>
- atof
- strtof
- strtod
- strtold
字符串转其他 <stdio.h>
- sscanf