Defined in header <cinttypes>  

std::intmax_t strtoimax( const char* nptr, char** endptr, int base );  (since C++11)  
std::uintmax_t strtoumax( const char* nptr, char** endptr, int base );  (since C++11) 
Interprets an integer value in a byte string pointed to by nptr
.
Discards any whitespace characters (as identified by calling isspace()
) until the first nonwhitespace character is found, then takes as many characters as possible to form a valid basen (where n=base) integer number representation and converts them to an integer value. The valid integer value consists of the following parts:
0
) indicating octal base (applies only when the base is 8
or 0
) 0x
or 0X
) indicating hexadecimal base (applies only when the base is 16
or 0
) The set of valid values for base is {0,2,3,...,36}. The set of valid digits for base2 integers is {0,1
}, for base3 integers is {0,1,2
}, and so on. For bases larger than 10
, valid digits include alphabetic characters, starting from Aa
for base11 integer, to Zz
for base36 integer. The case of the characters is ignored.
Additional numeric formats may be accepted by the currently installed C locale
.
If the value of base is 0
, the numeric base is autodetected: if the prefix is 0
, the base is octal, if the prefix is 0x
or 0X
, the base is hexadecimal, otherwise the base is decimal.
If the minus sign was part of the input sequence, the numeric value calculated from the sequence of digits is negated as if by unary minus in the result type.
The functions sets the pointer pointed to by endptr
to point to the character past the last character interpreted. If endptr
is NULL
, it is ignored.
If the nptr
is empty or does not have the expected form, no conversion is performed, and (if enptr
is not NULL
) the value of nptr
is stored in the object pointed to by endptr
.
nptr    pointer to the nullterminated byte string to be interpreted 
endptr    pointer to a pointer to character. 
base    base of the interpreted integer value 
str
is returned. errno
to ERANGE
) and INTMAX_MAX
, INTMAX_MIN
, UINTMAX_MAX
or 0
is returned, as appropriate. 0
is returned. #include <iostream> #include <string> #include <cinttypes> int main() { std::string str = "helloworld"; std::intmax_t val = std::strtoimax(str.c_str(), nullptr, 36); std::cout << str << " in base 36 is " << val << " in base 10\n"; char* nptr; val = std::strtoimax(str.c_str(), &nptr, 30); if(nptr != &str[0] + str.size()) std::cout << str << " in base 30 is invalid." << " The first invalid digit is " << *nptr << '\n'; }
Output:
helloworld in base 36 is 1767707668033969 in base 10 helloworld in base 30 is invalid. The first invalid digit is w
(C++11)(C++11)  converts a wide string to std::intmax_t or std::uintmax_t (function) 
converts a byte string to an integer value (function) 

converts a byte string to an unsigned integer value (function) 

C documentation for strtoimax, strtoumax 
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