Difference between revisions of "cpp/string/basic string/stol"

Latest revision as of 19:02, 7 August 2023

Defined in header `<string>`
int stoi ( const std::string& str, std::size_t* pos = nullptr, int base = 10 );	(1)	(since C++11)
int stoi ( const std::wstring& str, std::size_t* pos = nullptr, int base = 10 );	(2)	(since C++11)
long stol ( const std::string& str, std::size_t* pos = nullptr, int base = 10 );	(3)	(since C++11)
long stol ( const std::wstring& str, std::size_t* pos = nullptr, int base = 10 );	(4)	(since C++11)
long long stoll( const std::string& str, std::size_t* pos = nullptr, int base = 10 );	(5)	(since C++11)
long long stoll( const std::wstring& str, std::size_t* pos = nullptr, int base = 10 );	(6)	(since C++11)

Interprets a signed integer value in the string str.

Let ptr be an internal (to the conversion functions) pointer of type char* (1,3,5) or wchar_t* (2,4,6), accordingly.

1) Calls std::strtol(str.c_str(), &ptr, base).

2) Calls std::wcstol(str.c_str(), &ptr, base).

3) Calls std::strtol(str.c_str(), &ptr, base).

4) Calls std::wcstol(str.c_str(), &ptr, base).

5) Calls std::strtoll(str.c_str(), &ptr, base).

6) Calls std::wcstoll(str.c_str(), &ptr, base).

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) integer number representation and converts them to an integer value. The valid 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.

If pos is not a null pointer, then ptr will receive an address of the first unconverted character in str.c_str(), and the index of that character will be calculated and stored in *pos, giving the number of characters that were processed by the conversion.

#include <iomanip>
#include <iostream>
#include <stdexcept>
#include <string>
#include <utility>
 
int main()
{
    const auto data =
    {
        "45",
        "+45",
        " -45",
        "3.14159",
        "31337 with words",
        "words and 2",
        "12345678901",
    };
 
    for (const std::string s : data)
    {
        std::size_t pos{};
        try
        {
            std::cout << "std::stoi(" << std::quoted(s) << "): ";
            const int i{std::stoi(s, &pos)};
            std::cout << i << "; pos: " << pos << '\n';
        }
        catch (std::invalid_argument const& ex)
        {
            std::cout << "std::invalid_argument::what(): " << ex.what() << '\n';
        }
        catch (std::out_of_range const& ex)
        {
            std::cout << "std::out_of_range::what(): " << ex.what() << '\n';
            const long long ll{std::stoll(s, &pos)};
            std::cout << "std::stoll(" << std::quoted(s) << "): " << ll
                      << "; pos: " << pos << '\n';
        }
    }
 
    std::cout << "\nCalling with different radixes:\n";
    for (const auto& [s, base] : {std::pair<const char*, int>
        {"11",  2}, {"22",  3}, {"33",  4}, {"77",  8},
        {"99", 10}, {"FF", 16}, {"jJ", 20}, {"Zz", 36}})
    {
        const int i{std::stoi(s, nullptr, base)};
        std::cout << "std::stoi(" << std::quoted(s)
                  << ", nullptr, " << base << "): " << i << '\n';
    }
}

Possible output:

std::stoi("45"): 45; pos: 2
std::stoi("+45"): 45; pos: 3
std::stoi(" -45"): -45; pos: 4
std::stoi("3.14159"): 3; pos: 1
std::stoi("31337 with words"): 31337; pos: 5
std::stoi("words and 2"): std::invalid_argument::what(): stoi
std::stoi("12345678901"): std::out_of_range::what(): stoi
std::stoll("12345678901"): 12345678901; pos: 11
 
Calling with different radixes:
std::stoi("11", nullptr, 2): 3
std::stoi("22", nullptr, 3): 8
std::stoi("33", nullptr, 4): 15
std::stoi("77", nullptr, 8): 63
std::stoi("99", nullptr, 10): 99
std::stoi("FF", nullptr, 16): 255
std::stoi("jJ", nullptr, 20): 399
std::stoi("Zz", nullptr, 36): 1295

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2009	C++11	std::out_of_range would not be thrown if std::strtol or std::strtoll sets errno to ERANGE	will throw

[edit] See also

stoulstoull (C++11)(C++11)	converts a string to an unsigned integer (function) [edit]
stofstodstold (C++11)(C++11)(C++11)	converts a string to a floating point value (function) [edit]
strtolstrtoll (C++11)	converts a byte string to an integer value (function) [edit]
strtoulstrtoull (C++11)	converts a byte string to an unsigned integer value (function) [edit]
strtoimaxstrtoumax (C++11)(C++11)	converts a byte string to std::intmax_t or std::uintmax_t (function) [edit]
from_chars (C++17)	converts a character sequence to an integer or floating-point value (function) [edit]
atoiatolatoll (C++11)	converts a byte string to an integer value (function) [edit]
to_string (C++11)	converts an integral or floating-point value to `string` (function) [edit]
to_wstring (C++11)	converts an integral or floating-point value to `wstring` (function) [edit]

@@ Line 4: / Line 4: @@
 {{dcl header|string}}
 {{dcl|num=1|since=c++11|1=
-int        stoi( const std::string& str,
+int       stoi ( const std::string& str,
                   std::size_t* pos = nullptr, int base = 10 );
 }}
 {{dcl|num=2|since=c++11|1=
-int        stoi( const std::wstring& str,
+int       stoi ( const std::wstring& str,
                   std::size_t* pos = nullptr, int base = 10 );
 }}
 {{dcl|num=3|since=c++11|1=
-long       stol( const std::string& str,
+long      stol ( const std::string& str,
                   std::size_t* pos = nullptr, int base = 10 );
 }}
 {{dcl|num=4|since=c++11|1=
-long       stol( const std::wstring& str,
+long      stol ( const std::wstring& str,
                   std::size_t* pos = nullptr, int base = 10 );
 }}

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Difference between revisions of "cpp/string/basic string/stol"

Latest revision as of 19:02, 7 August 2023

Contents

[edit] Parameters

[edit] Return value

[edit] Exceptions

[edit] Example

[edit] Defect reports

[edit] See also

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Toolbox

str	-	the string to convert
pos	-	address of an integer to store the number of characters processed
base	-	the number base