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

From cppreference.com
< cpp‎ | string‎ | basic string
(trying to make it clearer what *pos receives)
m (Minor tweak.)
 
(17 intermediate revisions by 7 users not shown)
Line 1: Line 1:
−
{{cpp/title| stoi | stol | stoll}}
+
{{cpp/title|stoi|stol|stoll}}
 
{{cpp/string/basic_string/navbar}}
 
{{cpp/string/basic_string/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
−
{{dcl header | string}}
+
{{dcl header|string}}
−
{{dcl | num=1 | since=c++11 | 1=
+
{{dcl|num=1|since=c++11|1=
−
int      stoi( const std::string& str, std::size_t* pos = 0, int base = 10 );
+
int      stoi ( const std::string& str,
−
int      stoi( const std::wstring& str, std::size_t* pos = 0, int base = 10 );
+
                std::size_t* pos = nullptr, int base = 10 );
 
}}
 
}}
−
{{dcl | num=2 | since=c++11 | 1=
+
{{dcl|num=2|since=c++11|1=
−
long      stol( const std::string& str, std::size_t* pos = 0, int base = 10 );
+
int       stoi ( const std::wstring& str,
−
long      stol( const std::wstring& str, std::size_t* pos = 0, int base = 10 );
+
                std::size_t* pos = nullptr, int base = 10 );
 
}}
 
}}
−
{{dcl | num=3 | since=c++11 | 1=
+
{{dcl|num=3|since=c++11|1=
−
long long stoll( const std::string& str, std::size_t* pos = 0, int base = 10 );
+
long      stol ( const std::string& str,
−
long long stoll( const std::wstring& str, std::size_t* pos = 0, int base = 10 );
+
                std::size_t* pos = nullptr, int base = 10 );
 +
}}
 +
{{dcl|num=4|since=c++11|1=
 +
long      stol ( const std::wstring& str,
 +
                std::size_t* pos = nullptr, int base = 10 );
 +
}}
 +
{{dcl|num=5|since=c++11|1=
 +
long long stoll( const std::string& str,
 +
                std::size_t* pos = nullptr, int base = 10 );
 +
}}
 +
{{dcl|num=6|since=c++11|1=
 +
long long stoll( const std::wstring& str,
 +
                std::size_t* pos = nullptr, int base = 10 );
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
−
Interprets a signed integer value in the string {{tt|str}}.
+
Interprets a signed integer value in the string {{c|str}}.
  
−
@1@ calls {{c|std::strtol(str.c_str(), &ptr, base)}} or {{c|std::wcstol(str.c_str(), &ptr, base)}}
+
Let {{c|ptr}} be an internal (to the conversion functions) pointer of type {{c/core|char*}} {{v|1,3,5}} or {{c/core|wchar_t*}} {{v|2,4,6}}, accordingly.
−
@2@ calls {{c|std::strtol(str.c_str(), &ptr, base)}} or {{c|std::wcstol(str.c_str(), &ptr, base)}}
+
−
@3@ calls {{c|std::strtoll(str.c_str(), &ptr, base)}} or {{c|std::wcstoll(str.c_str(), &ptr, base)}}
+
  
−
{{cpp/string/cvt str2int base | base=base}}
+
@1@ Calls {{c|std::strtol(str.c_str(), &ptr, base)}}.
 +
@2@ Calls {{c|std::wcstol(str.c_str(), &ptr, base)}}.
 +
@3@ Calls {{c|std::strtol(str.c_str(), &ptr, base)}}.
 +
@4@ Calls {{c|std::wcstol(str.c_str(), &ptr, base)}}.
 +
@5@ Calls {{c|std::strtoll(str.c_str(), &ptr, base)}}.
 +
@6@ Calls {{c|std::wcstoll(str.c_str(), &ptr, base)}}.
  
−
If {{tt|pos}} is not a null pointer, then a pointer {{tt|ptr}} - internal to the conversion functions - will receive the address of the first unconverted character in {{c|str.c_str()}}, and the index of that character will be calculated and stored in {{tt|*pos}}, giving the number of characters that were processed by the conversion.
+
{{cpp/string/cvt str2int base|base={{c|base}}}}
 +
 
 +
If {{c|pos}} is not a null pointer, then {{c|ptr}} will receive an address of the first unconverted character in {{c|str.c_str()}}, and the index of that character will be calculated and stored in {{c|*pos}}, giving the number of characters that were processed by the conversion.
  
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | str | the string to convert}}
+
{{par|str|the string to convert}}
−
{{par | pos | address of an integer to store the number of character processed}}
+
{{par|pos|address of an integer to store the number of characters processed}}
−
{{par | base | the number base}}
+
{{par|base|the number base}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
−
The string converted to the specified signed integer type.  
+
Integer value corresponding to the content of {{c|str}}.
  
 
===Exceptions===
 
===Exceptions===
−
* {{lc|std::invalid_argument}} if no conversion could be performed
+
* {{lc|std::invalid_argument}} if no conversion could be performed.
−
* {{lc|std::out_of_range}} if the converted value would fall out of the range of the result type or if the underlying function (std::strtol or std::strtoll) sets {{c|errno}} to {{c|ERANGE}}.
+
* {{lc|std::out_of_range}} if the converted value would fall out of the range of the result type or if the underlying function ({{lc|std::strtol}} or {{lc|std::strtoll}}) sets {{lc|errno}} to {{lc|ERANGE}}.
  
 
===Example===
 
===Example===
 
{{example|
 
{{example|
−
| code=  
+
|code=
 +
#include <iomanip>
 
#include <iostream>
 
#include <iostream>
 +
#include <stdexcept>
 
#include <string>
 
#include <string>
−
+
#include <utility>
 +
 
 
int main()
 
int main()
 
{
 
{
−
     std::string str1 = "45";
+
     const auto data =
−
    std::string str2 = "3.14159";
+
    {
−
    std::string str3 = "31337 with words";
+
        "45",
−
    std::string str4 = "words and 2";
+
        "+45",
 +
        " -45",
 +
        "3.14159",
 +
        "31337 with words",
 +
        "words and 2",
 +
        "12345678901",
 +
    };
 
      
 
      
−
     int myint1 = std::stoi(str1);
+
     for (const std::string s : data)
−
     int myint2 = std::stoi(str2);
+
     {
−
    int myint3 = std::stoi(str3);
+
        std::size_t pos{};
−
    // error: 'std::invalid_argument'
+
        try
−
    // int myint4 = std::stoi(str4);
+
        {
 +
            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 << "std::stoi(\"" << str1 << "\") is " << myint1 << '\n';
+
     std::cout << "\nCalling with different radixes:\n";
−
     std::cout << "std::stoi(\"" << str2 << "\") is " << myint2 << '\n';
+
     for (const auto& [s, base] : {std::pair<const char*, int>
−
     std::cout << "std::stoi(\"" << str3 << "\") is " << myint3 << '\n';
+
        {"11",  2}, {"22",  3}, {"33",  4}, {"77",  8},
−
    //std::cout << "std::stoi(\"" << str4 << "\") is " << myint4 << '\n';
+
        {"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';
 +
    }
 
}
 
}
−
| output=
+
|p=true
−
std::stoi("45") is 45
+
|output=
−
std::stoi("3.14159") is 3
+
std::stoi("45"): 45; pos: 2
−
std::stoi("31337 with words") is 31337
+
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
 
}}
 
}}
 +
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=2009|std=C++11|before={{lc|std::out_of_range}} would not be thrown if<br>{{lc|std::strtol}} or {{lc|std::strtoll}} sets {{lc|errno}} to {{lc|ERANGE}}|after=will throw}}
 +
{{dr list end}}
  
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/string/byte/dsc atoi}}
+
{{dsc inc|cpp/string/basic_string/dsc stoul}}
−
{{dsc inc | cpp/string/basic_string/dsc stoul}}
+
{{dsc inc|cpp/string/basic_string/dsc stof}}
−
{{dsc inc | cpp/string/basic_string/dsc stof}}
+
{{dsc inc|cpp/string/byte/dsc strtol}}
−
{{dsc inc | cpp/string/basic_string/dsc to_string}}
+
{{dsc inc|cpp/string/byte/dsc strtoul}}
 +
{{dsc inc|cpp/string/byte/dsc strtoimax}}
 +
{{dsc inc|cpp/utility/dsc from_chars}}
 +
{{dsc inc|cpp/string/byte/dsc atoi}}
 +
{{dsc inc|cpp/string/basic_string/dsc to_string}}
 +
{{dsc inc|cpp/string/basic_string/dsc to_wstring}}
 
{{dsc end}}
 
{{dsc end}}
  
−
[[de:cpp/string/basic string/stol]]
+
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
−
[[es:cpp/string/basic string/stol]]
+
−
[[fr:cpp/string/basic string/stol]]
+
−
[[it:cpp/string/basic string/stol]]
+
−
[[ja:cpp/string/basic string/stol]]
+
−
[[pt:cpp/string/basic string/stol]]
+
−
[[ru:cpp/string/basic string/stol]]
+
−
[[zh:cpp/string/basic string/stol]]
+

Latest revision as of 19:02, 7 August 2023

 
C++
 
Strings library
 
std::basic_string
Member functions
(C++23)
Element access
(DR*)
(DR*)
(C++17)
Iterators
(C++11)
(C++11)
(C++11)
(C++11)
Capacity
(DR*)
Modifiers
(C++23)
(DR*)
(C++23)
(C++23)
(C++23)  
Search
Operations
(C++20)
(C++20)
(C++23)
Constants
Non-member functions
(C++20)(C++20)
I/O
Comparison
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Numeric conversions
stoistolstoll
(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)(C++11)
(C++11)
(C++11)
Literals
(C++14)
Helper classes
(C++11)
Deduction guides (C++17)

 
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.

Contents

[edit] Parameters

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

[edit] Return value

Integer value corresponding to the content of str.

[edit] Exceptions

[edit] Example

Run this code
#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

(C++11)(C++11)
 converts a string to an unsigned integer
(function) [edit]
(C++11)(C++11)(C++11)
 converts a string to a floating point value
(function) [edit]
(C++11)
 converts a byte string to an integer value
(function) [edit]
(C++11)
 converts a byte string to an unsigned integer value
(function) [edit]
(C++11)(C++11)
 converts a byte string to std::intmax_t or std::uintmax_t
(function) [edit]
(C++17)
 converts a character sequence to an integer or floating-point value
(function) [edit]
(C++11)
 converts a byte string to an integer value
(function) [edit]
(C++11)
 converts an integral or floating-point value to string
(function) [edit]
(C++11)
 converts an integral or floating-point value to wstring
(function) [edit]
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