stdlib.h头文件中的函数
atof Convert string to double (function)
atoi Convert string to integer (function)
atol Convert string to long integer (function)
strtod Convert string to double (function)
strtol Convert string to long integer (function)
strtoul Convert string to unsigned long integer (function)
ctype.h头文件中的函数
isalnum Check if character is alphanumeric (function)
isalpha Check if character is alphabetic (function)
iscntrl Check if character is a control character (function)
isdigit Check if character is decimal digit (function)
isgraph Check if character has graphical representation using locale (function template)
islower Check if character is lowercase letter (function)
isprint Check if character is printable (function)
ispunct Check if character is a punctuation character (function)
isspace Check if character is a white-space (function)
isupper Check if character is uppercase letter (function)
isxdigit Check if character is hexadecimal digit (function)
用判断是否是数字的函数,判断数字,再判断小数点,然后再将分离出来的字符串,转化成数字。