The strtoumax function converts a string of ASCII characters pointed to by nptr to the appropriate unsigned numeric values. strtoumax is a synonym for strtoull The function recognizes strings in various formats, depending on the value of the base. Any leading white-space characters (as defined by isspace in <ctype.h>) in the given string are ignored. The function recognizes an optional plus or minus sign, then a sequence of digits or letters that may represent an integer constant according to the value of the base. The first unrecognized character ends the conversion and is pointed to by endptr. If base is 16, leading zeros after the optional sign are ignored, and 0x or 0X is ignored. If base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant: after the optional sign, a leading 0 indicates octal conversion, a leading 0x or 0X indicates hexadecimal conversion, and any other combination of leading characters indicates decimal conversion.