在Linux下，使用
gets(cmd)
函数报错：warning: the 'gets' function is dangerous and should not be used.
解决办法：采用
fgets(cmd,100,stdin);//100为size
问题解决！
fgets从stdin中读字符，直至读到换行符或文件结束，但一次最多读size个字符。读出的字符连同换行符存入缓冲区cmd中。返回指向cmd的指针。
gets把从stdin中输入的一行信息存入cmd中，然后将换行符置换成串结尾符NULL。用户要保证缓冲区的长度大于或等于最大的行长。
gets的详细解释：
char * gets ( char * str );//Get string from stdin
Reads characters from stdin and stores them as a string into str until a newline character ('\n') or the End-of-File is reached.
The ending newline character ('\n') is not included in the string.
A null character ('\0') is automatically appended after the last character copied to str to signal the end of the C string.
Notice that gets does not behave exactly as fgets does with stdin as argument: First, the ending newline character is not included with gets while with fgets it is. And second, gets does not let you specify a limit on how many characters are to be read, so you must be careful with the size of the array pointed by str to avoid buffer overflows.
说明：红色部分很好地解释了“the 'gets' function is dangerous and should not be used”这个warning的原因。
参考链接：http://www.cplusplus.com/reference/clibrary/cstdio/gets/