strtoq() converts the string nptr to a quadt value. The conversion is done according to the given base, which shall be between 2 and 36 inclusive, or be the special value 0.
nptr may begin with an arbitrary amount of white space (as determined by isspace()(3)), followed by a single optional + or - sign character. If base is 0 or 16, the string may then include a 0x prefix, and the number will be read in base 16; otherwise, a 0 base is taken as 10 (decimal), unless the next character is 0, in which case it is taken as 8 (octal).
The remainder of the string is converted to a long value in the obvious manner, stopping at the first character which is not a valid digit in the given base. (In bases above 10, the letter A in either upper or lower case represents 10, B represents 11, and so forth, with Z representing 35.)
strtoq() returns the result of the conversion,
unless the value would underflow or overflow. If an underflow occurs,
an overflow occurs, strtoq() returns
QUAD_MAX. In both cases, the global variable
errno is set to ERANGE.