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std::strtoul,std::strtoull(3) C++ Standard Libary std::strtoul,std::strtoull(3)


std::strtoul,std::strtoull - std::strtoul,std::strtoull


Defined in header <cstdlib>
unsigned long strtoul( const char *str, char **str_end, int base );
unsigned long long strtoull( const char *str, char **str_end, int (since C++11)
base );

Interprets an unsigned integer value in a byte string pointed to by str.

Discards any whitespace characters (as identified by calling std::isspace) until the
first non-whitespace character is found, then takes as many characters as possible
to form a valid base-n (where n=base) unsigned integer number representation and
converts them to an integer value. The valid unsigned integer value consists of the
following parts:

* (optional) plus or minus sign
* (optional) prefix (0) indicating octal base (applies only when the base is 8 or
* (optional) prefix (0x or 0X) indicating hexadecimal base (applies only when the
base is 16 or 0)
* a sequence of digits

The set of valid values for base is {0,2,3,...,36}. The set of valid digits for
base-2 integers is {0,1}, for base-3 integers is {0,1,2}, and so on. For bases
larger than 10, valid digits include alphabetic characters, starting from Aa for
base-11 integer, to Zz for base-36 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 auto-detected: 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, which
applies unsigned integer wraparound rules.

The functions sets the pointer pointed to by str_end to point to the character past
the last character interpreted. If str_end is a null pointer, it is ignored.


str - pointer to the null-terminated byte string to be interpreted
str_end - pointer to a pointer to character.
base - base of the interpreted integer value

Return value

Integer value corresponding to the contents of str on success. If the converted
value falls out of range of corresponding return type, range error occurs and
ULONG_MAX or ULLONG_MAX is returned. If no conversion can be performed, 0 is


// Run this code

#include <iostream>
#include <string>
#include <errno.h>
#include <cstdlib>

int main()
const char* p = "10 200000000000000000000000000000 30 -40";
char *end;
std::cout << "Parsing '" << p << "':\n";
for (unsigned long i = std::strtoul(p, &end, 10);
p != end;
i = std::strtoul(p, &end, 10))
std::cout << "'" << std::string(p, end-p) << "' -> ";
p = end;
if (errno == ERANGE){
std::cout << "range error, got ";
errno = 0;
std::cout << i << '\n';

Possible output:

Parsing '10 200000000000000000000000000000 30 -40':
'10' -> 10
' 200000000000000000000000000000' -> range error, got 18446744073709551615
' 30' -> 30
' -40' -> 18446744073709551576

See also

stoull converts a string to an unsigned integer
(C++11) (function)
strtol converts a byte string to an integer value
strtoll (function)
strtoumax converts a byte string to std::intmax_t or std::uintmax_t
(C++11) (function)
wcstoul converts a wide string to an unsigned integer value
wcstoull (function)
strtof converts a byte string to a floating point value
strtod (function)
from_chars converts a character sequence to an integer or floating-point value
(C++17) (function)
atol converts a byte string to an integer value
atoll (function)