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<string> functions

  • บทความ

getline
stod
stof
stoi
stol
stold
stoll
stoul
stoull
swap
to_string
to_wstring

getline

Extract strings from the input stream line-by-line.

// (1) delimiter as parameter
template <class CharType, class Traits, class Allocator>
basic_istream<CharType, Traits>& getline(
    basic_istream<CharType, Traits>& in_stream,
    basic_string<CharType, Traits, Allocator>& str,
    CharType delimiter);

template <class CharType, class Traits, class Allocator>
basic_istream<CharType, Traits>& getline(
    basic_istream<CharType, Traits>&& in_stream,
    basic_string<CharType, Traits, Allocator>& str,
    const CharType delimiter);

// (2) default delimiter used
template <class CharType, class Traits, class Allocator>
basic_istream<CharType, Traits>& getline(
    basic_istream<CharType, Traits>& in_stream,
    basic_string<CharType, Traits, Allocator>& str);

template <class Allocator, class Traits, class Allocator>
basic_istream<Allocator, Traits>& getline(
    basic_istream<Allocator, Traits>&& in_stream,
    basic_string<Allocator, Traits, Allocator>& str);

Parameters

in_stream
The input stream from which a string is to be extracted.

str
The string into which are read the characters from the input stream.

delimiter
The line delimiter.

Return Value

The input stream in_stream.

Remarks

The pair of function signatures marked (1) extract characters from in_stream until delimiter is found, storing them in str.

The pair of function signatures marked (2) use newline as the default line delimiter and behave as getline(in_stream, str, in_stream. widen('\n')).

The second function of each pair is an analog to the first one to support rvalue references.

Extraction stops when one of the following occurs:

  • At end of file, in which case the internal state flag of in_stream is set to ios_base::eofbit.

  • After the function extracts an element that compares equal to delimiter. The element doesn't get put back or appended to the controlled sequence.

  • After the function extracts str.max_size elements. The internal state flag of in_stream is set to ios_base::failbit.

  • Some other error other than the ones previously listed; the internal state flag of in_stream is set to ios_base::badbit.

For information about internal state flags, see ios_base::iostate.

If the function extracts no elements, the internal state flag of in_stream is set to ios_base::failbit. In any case, getline returns in_stream.

If an exception is thrown, in_stream and str are left in a valid state.

Example

The following code demonstrates getline() in two modes: first with the default delimiter (newline) and second with a whitespace as delimiter. The end-of-file character (CTRL-Z on the keyboard) is used to control termination of the while loops. This value sets the internal state flag of cin to eofbit, which must be cleared with basic_ios::clear() before the second while loop will work properly.

// compile with: /EHsc /W4
#include <string>
#include <iostream>
#include <vector>

using namespace std;

int main()
{
    string str;
    vector<string> v1;
    cout << "Enter a sentence, press ENTER between sentences. (Ctrl-Z to stop): " << endl;
    // Loop until end-of-file (Ctrl-Z) is input, store each sentence in a vector.
    // Default delimiter is the newline character.
    while (getline(cin, str)) {
        v1.push_back(str);
    }

    cout << "The following input was stored with newline delimiter:" << endl;
    for (const auto& p : v1) {
        cout << p << endl;
    }

    cin.clear();

    vector<string> v2;
    // Now try it with a whitespace delimiter
    while (getline(cin, str, ' ')) {
        v2.push_back(str);
    }

    cout << "The following input was stored with whitespace as delimiter:" << endl;
    for (const auto& p : v2) {
        cout << p << endl;
    }
}

stod

Converts a character sequence to a double.

double stod(
    const string& str,
    size_t* idx = 0);

double stod(
    const wstring& str,
    size_t* idx = 0
;

Parameters

str
The character sequence to be converted.

idx
The index value of the first unconverted character.

Return Value

The double value.

Remarks

The function converts the sequence of elements in str to a value of type double as if by calling strtod( str.c_str(), _Eptr), where _Eptr is an object internal to the function. If str.c_str() == *_Eptr, it throws an object of type invalid_argument. If such a call would set errno, it throws an object of type out_of_range. Otherwise, if idx isn't a null pointer, the function stores *_Eptr - str.c_str() in *idx and returns the value.

stof

Converts a character sequence to a float.

float stof(
    const string& str,
    size_t* idx = 0);

float stof(
    const wstring& str,
    size_t* idx = 0);

Parameters

str
The character sequence to be converted.

idx
The index value of the first unconverted character.

Return Value

The float value.

Remarks

The function converts the sequence of elements in str to a value of type float as if by calling strtof( str.c_str(), _Eptr), where _Eptr is an object internal to the function. If str.c_str() == *_Eptr, it throws an object of type invalid_argument. If such a call would set errno, it throws an object of type out_of_range. Otherwise, if idx isn't a null pointer, the function stores *_Eptr - str.c_str() in *idx and returns the value.

stoi

Converts a character sequence to an integer.

int stoi(
    const string& str,
    size_t* idx = 0,
    int base = 10);

int stoi(
    const wstring& str,
    size_t* idx = 0,
    int base = 10);

Return Value

The integer value.

Parameters

str
The character sequence to be converted.

idx
The index value of the first unconverted character.

base
The number base to use.

Remarks

The function stoi converts the sequence of characters in str to a value of type int and returns the value. For example, when passed a character sequence "10", the value returned by stoi is the integer 10.

stoi behaves similarly to the function strtol for single-byte characters when it's called in the manner strtol( str.c_str(), _Eptr, idx), where _Eptr is an object internal to the function; or wcstol for wide characters, when it's called in similar manner, wcstol(Str.c_str(), _Eptr, idx). For more information, see strtol, wcstol, _strtol_l, _wcstol_l.

If str.c_str() == *_Eptr, stoi throws an object of type invalid_argument. If such a call would set errno, or if the returned value can't be represented as an object of type int, it throws an object of type out_of_range. Otherwise, if idx isn't a null pointer, the function stores *_Eptr - str.c_str() in *idx.

stol

Converts a character sequence to a long.

long stol(
    const string& str,
    size_t* idx = 0,
    int base = 10);

long stol(
    const wstring& str,
    size_t* idx = 0,
    int base = 10);

Parameters

str
The character sequence to be converted.

idx
The index value of the first unconverted character.

base
The number base to use.

Return Value

The long-integer value.

Remarks

The function converts the sequence of elements in str to a value of type long as if by calling strtol( str.c_str(), _Eptr, idx), where _Eptr is an object internal to the function. If str.c_str() == *_Eptr, it throws an object of type invalid_argument. If such a call would set errno, it throws an object of type out_of_range. Otherwise, if idx isn't a null pointer, the function stores *_Eptr - str.c_str() in *idx and returns the value.

stold

Converts a character sequence to a long double.

double stold(
    const string& str,
    size_t* idx = 0);

double stold(
    const wstring& str,
    size_t* idx = 0);

Parameters

str
The character sequence to be converted.

idx
The index value of the first unconverted character.

Return Value

The long double value.

Remarks

The function converts the sequence of elements in str to a value of type long double as if by calling strtold( str.c_str(), _Eptr), where _Eptr is an object internal to the function. If str.c_str() == *_Eptr, it throws an object of type invalid_argument. If such a call would set errno, it throws an object of type out_of_range. Otherwise, if idx isn't a null pointer, the function stores *_Eptr - str.c_str() in *idx and returns the value.

stoll

Converts a character sequence to a long long.

long long stoll(
    const string& str,
    size_t* idx = 0,
    int base = 10);

long long stoll(
    const wstring& str,
    size_t* idx = 0,
    int base = 10);

Parameters

str
The character sequence to be converted.

idx
The index value of the first unconverted character.

base
The number base to use.

Return Value

The long long value.

Remarks

The function converts the sequence of elements in str to a value of type long long as if by calling strtoll( str.c_str(), _Eptr, idx), where _Eptr is an object internal to the function. If str.c_str() == *_Eptr, it throws an object of type invalid_argument. If such a call would set errno, it throws an object of type out_of_range. Otherwise, if idx isn't a null pointer, the function stores *_Eptr - str.c_str() in *idx and returns the value.

stoul

Converts a character sequence to an unsigned long.

unsigned long stoul(
    const string& str,
    size_t* idx = 0,
    int base = 10);

unsigned long stoul(
    const wstring& str,
    size_t* idx = 0,
    int base = 10);

Parameters

str
The character sequence to be converted.

idx
The index value of the first unconverted character.

base
The number base to use.

Return Value

The unsigned long-integer value.

Remarks

The function converts the sequence of elements in str to a value of type unsigned long as if by calling strtoul( str.c_str(), _Eptr, idx), where _Eptr is an object internal to the function. If str.c_str() == *_Eptr, it throws an object of type invalid_argument. If such a call would set errno, it throws an object of type out_of_range. Otherwise, if idx isn't a null pointer, the function stores *_Eptr - str.c_str() in *idx and returns the value.

stoull

Converts a character sequence to an unsigned long long.

unsigned long long stoull(
    const string& str,
    size_t* idx = 0,
    int base = 10);

unsigned long long stoull(
    const wstring& str,
    size_t* idx = 0,
    int base = 10);

Parameters

str
The character sequence to be converted.

idx
The index value of the first unconverted character.

base
The number base to use.

Return Value

The unsigned long long value.

Remarks

The function converts the sequence of elements in str to a value of type unsigned long long as if by calling strtoull( str.c_str(), _Eptr, idx), where _Eptr is an object internal to the function. If str.c_str() == *_Eptr, it throws an object of type invalid_argument. If such a call would set errno, it throws an object of type out_of_range. Otherwise, if idx isn't a null pointer, the function stores *_Eptr - str.c_str() in *idx and returns the value.

swap

Exchanges the arrays of characters of two strings.

template <class Traits, class Allocator>
void swap(basic_string<CharType, Traits, Allocator>& left, basic_string<CharType, Traits, Allocator>& right);

Parameters

left
One string whose elements are to be swapped with the elements of another string.

right
The other string whose elements are to be swapped with the first string.

Remarks

The template function executes the specialized member function left.swap(right) for strings, which guarantees constant complexity.

Example

// string_swap.cpp
// compile with: /EHsc
#include <string>
#include <iostream>

int main( )
{
   using namespace std;
   // Declaring an object of type basic_string<char>
   string s1 ( "Tweedledee" );
   string s2 ( "Tweedledum" );
   cout << "Before swapping string s1 and s2:" << endl;
   cout << "The basic_string s1 = " << s1 << "." << endl;
   cout << "The basic_string s2 = " << s2 << "." << endl;

   swap ( s1 , s2 );
   cout << "\nAfter swapping string s1 and s2:" << endl;
   cout << "The basic_string s1 = " << s1 << "." << endl;
   cout << "The basic_string s2 = " << s2 << "." << endl;
}

Before swapping string s1 and s2:
The basic_string s1 = Tweedledee.
The basic_string s2 = Tweedledum.

After swapping string s1 and s2:
The basic_string s1 = Tweedledum.
The basic_string s2 = Tweedledee.

to_string

Converts a value to a string.

string to_string(int value);
string to_string(unsigned int value);
string to_string(long value);
string to_string(unsigned long value);
string to_string(long long value);
string to_string(unsigned long long value);
string to_string(float value);
string to_string(double value);
string to_string(long double value);

Parameters

value
The value to be converted.

Return Value

The string that represents the value.

Remarks

The function converts value to a sequence of elements stored in an array object Buf internal to the function as if by calling sprintf(Buf, Fmt, value), where Fmt is

  • "%d" if value is of type int

  • "%u" if value is of type unsigned int

  • "%ld" if value is of type long

  • "%lu" if value is of type unsigned long

  • "%lld" if value is of type long long

  • "%llu" if value is of type unsigned long long

  • "%f" if value is of type float or double

  • "%Lf" if value is of type long double

The function returns string(Buf).

to_wstring

Converts a value to a wide string.

wstring to_wstring(int value);
wstring to_wstring(unsigned int value);
wstring to_wstring(long value);
wstring to_wstring(unsigned long value);
wstring to_wstring(long long value);
wstring to_wstring(unsigned long long value);
wstring to_wstring(float value);
wstring to_wstring(double value);
wstring to_wstring(long double value);

Parameters

value
The value to be converted.

Return Value

The wide string that represents the value.

Remarks

The function converts value to a sequence of elements stored in an array object Buf internal to the function as if by calling swprintf(Buf, Len, Fmt, value), where Fmt is

  • L"%d" if value is of type int

  • L"%u" if value is of type unsigned int

  • L"%ld" if value is of type long

  • L"%lu" if value is of type unsigned long

  • L"%lld" if value is of type long long

  • L"%llu" if value is of type unsigned long long

  • L"%f" if value is of type float or double

  • L"%Lf" if value is of type long double

The function returns wstring(Buf).

See also

<string>