std::strtoul, std::strtoull

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

Null-terminated byte strings

Functions
Character manipulation
isalnum isalpha islower isupper isdigit isxdigit isblank (C++11)	iscntrl isgraph isspace isprint ispunct tolower toupper
Conversions to numeric formats
atof atoiatolatoll (C++11) strtolstrtoll (C++11)	strtoulstrtoull (C++11) strtofstrtodstrtold (C++11)(C++11) strtoimaxstrtouimax (C++11)(C++11)
String manipulation
strcpy strncpy strxfrm	strcat strncat
String examination
strlen strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtok
Memory manipulation
memchr memcmp memset	memcpy memmove
Miscellaneous
strerror

 

Defined in header <cstdlib>
unsigned long      strtoul ( const char* str, char** str_end, int base );	(1)
unsigned long long strtoull( const char* str, char** str_end, int base );	(2)	(since C++11)

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 ​0​)
• (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.

Parameters

str	-	pointer to the null-terminated byte string to be interpreted
str_end	-	pointer to a pointer to character, might be set to a position past the last character interpreted
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 (errno is set to ERANGE) and ULONG_MAX or ULLONG_MAX is returned. If no conversion can be performed, ​0​ is returned.

Example

Run this code

#include <cstdlib>
#include <errno.h>
#include <iostream>
#include <string>
 
int main()
{
    const char* p = "10 200000000000000000000000000000 30 -40 - 42";
    char* end = nullptr;
    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)
        {
            errno = 0;
            std::cout << "range error, got ";
        }
        std::cout << i << '\n';
    }
    std::cout << "After the loop p points to '" << p << "'\n";
}

Possible output:

Parsing '10 200000000000000000000000000000 30 -40 - 42':
'10' -> 10
' 200000000000000000000000000000' -> range error, got 18446744073709551615
' 30' -> 30
' -40' -> 18446744073709551576
After the loop p points to ' - 42'

See also

stoulstoull (C++11)(C++11)	converts a string to an unsigned integer (function)
strtolstrtoll (C++11)	converts a byte string to an integer value (function)
strtoimaxstrtoumax (C++11)(C++11)	converts a byte string to std::intmax_t or std::uintmax_t (function)
wcstoulwcstoull	converts a wide string to an unsigned integer value (function)
strtofstrtodstrtold	converts a byte string to a floating-point value (function)
from_chars (C++17)	converts a character sequence to an integer or floating-point value (function)
atoiatolatoll (C++11)	converts a byte string to an integer value (function)
C documentation for strtoul, strtoull