Freigeben über

<string> functions

  • Artikel

 

The latest version of this topic can be found at <string> functions.

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>& is,  
    basic_string<CharType, Traits, Allocator>& str, CharType delim);

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

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

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

Parameters

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

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

delim
The line delimiter.

Return Value

The input stream is.

Remarks

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

The pair of function signatures marked (2) use newline as the default line delimiter and behave as getline( is, str, is. 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 is is set to ios_base::eofbit.

  • After the function extracts an element that compares equal to delim, in which case the element is neither put back nor appended to the controlled sequence.

  • After the function extracts str.max_size elements, in which case the internal state flag of is is set to ios_base::failbit.

  • Some other error other than those previously listed, in which case the internal state flag of is 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 is is set to ios_base::failbit. In any case, getline returns is.

If an exception is thrown, is 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 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

Parameter Description
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 val 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 is not a null pointer, the function stores *_Eptr - str.c_str() in *_Idx and returns val.

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

Parameter Description
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 val 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 is not a null pointer, the function stores *_Eptr - str.c_str() in *_Idx and returns val.

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

Parameter Description
str The character sequence to be converted.
_Idx Contains the index of the first unconverted character on return.
_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 is called in the manner strtol( str.c_str(), _Eptr, _Base), where _Eptr is an object internal to the function; or wcstol for wide characters, when it is called in similar manner, wcstol(Str.c_str(), _Eptr, _Base). 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 cannot be represented as an object of type int, it throws an object of type out_of_range. Otherwise, if _Idx is not 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

Parameter Description
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 val of type long as if by calling strtol( str.c_str(), _Eptr, _Base), 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 is not a null pointer, the function stores *_Eptr - str.c_str() in *_Idx and returns val.

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

Parameter Description
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 val 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 is not a null pointer, the function stores *_Eptr - str.c_str() in *_Idx and returns val.

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

Parameter Description
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 val of type long long as if by calling strtoll( str.c_str(), _Eptr, _Base), 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 is not a null pointer, the function stores *_Eptr - str.c_str() in *_Idx and returns val.

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

Parameter Description
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 val of type unsigned long as if by calling strtoul( str.c_str(), _Eptr, _Base), 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 is not a null pointer, the function stores *_Eptr - str.c_str() in *_Idx and returns val.

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

Parameter Description
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 val of type unsigned long long as if by calling strtoull( str.c_str(), _Eptr, _Base), 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 is not a null pointer, the function stores *_Eptr - str.c_str() in *_Idx and returns val.

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 those 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 Val);

string to_string(unsigned int Val);

string to_string(long Val);

string to_string(unsigned long Val);

string to_string(long long Val);

string to_string(unsigned long long Val);

string to_string(float Val);

string to_string(double Val);

string to_string(long double Val);

Parameters

Parameter Description
Val The value to be converted.

Return Value

The string that represents the value.

Remarks

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

  • "%d" if Val has type int

  • "%u" if Val has type unsigned int

  • "%ld" if Val has type long

  • "%lu" if Val has type unsigned long

  • "%lld" if Val has type long long

  • "%llu" if Val has type unsigned long long

  • "%f" if Val has type float or double

  • "%Lf" if Val has type long double

The function returns string(Buf).

to_wstring

Converts a value to a wide string.

wstring to_wstring(int Val);

wstring to_wstring(unsigned int Val);

wstring to_wstring(long Val);

wstring to_wstring(unsigned long Val);

wstring to_wstring(long long Val);

wstring to_wstring(unsigned long long Val);

wstring to_wstring(float Val);

wstring to_wstring(double Val);

wstring to_wstring(long double Val);

Parameters

Parameter Description
Val The value to be converted.

Return Value

The wide string that represents the value.

Remarks

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

  • L"%d" if Val has type int

  • L"%u" if Val has type unsigned int

  • L"%ld" if Val has type long

  • L"%lu" if Val has type unsigned long

  • L"%lld" if Val has type long long

  • L"%llu" if Val has type unsigned long long

  • L"%f" if Val has type float or double

  • L"%Lf" if Val has type long double

The function returns wstring(Buf).

See Also

<string>