std::ws

 

C++

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Feature test macros (C++20)

Language support library

Concepts library (C++20)

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Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (deprecated in C++98)

basic_syncbuf (C++20)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

File I/O

basic_ifstream

basic_ofstream

basic_fstream

String I/O

basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (deprecated in C++98)

ostrstream (deprecated in C++98)

strstream (deprecated in C++98)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

Input/output manipulators

Floating-point formatting
showpointnoshowpoint setprecision	fixedscientifichexfloatdefaultfloat (C++11)(C++11)
Integer formatting
setbase showbasenoshowbase	dechexoct
Boolean formatting
boolalphanoboolalpha
Field width and fill control
setfill setw	internalleftright
Other formatting
showposnoshowpos	uppercasenouppercase
Whitespace processing
ws ends	skipwsnoskipws
Output flushing
flush endl flush_emit (C++20)	unitbufnounitbuf emit_on_flushnoemit_on_flush (C++20)(C++20)
Status flags manipulation
resetiosflags	setiosflags
Time and money I/O
get_money (C++11) get_time (C++11)	put_money (C++11) put_time (C++11)
Quoted manipulator
quoted (C++14)

 

Defined in header <istream>
template< class CharT, class Traits > std::basic_istream<CharT, Traits>& ws( std::basic_istream<CharT, Traits>& is );

Discards leading whitespace from an input stream.

Behaves as an UnformattedInputFunction, except that is.gcount() is not modified. After constructing and checking the sentry object, extracts characters from the stream and discards them until any one of the following conditions occurs:

• end of file condition occurs in the input sequence (in which case the function calls setstate(eofbit) but does not set failbit; this does not apply if the eofbit is already set on is prior to the call to ws, in which case the construction of the sentry object would set failbit).

• the next available character c in the input sequence is not whitespace as determined by std::isspace(c, is.getloc()). The non-whitespace character is not extracted.

This is an input-only I/O manipulator, it may be called with an expression such as in >> std::ws for any in of type std::basic_istream.

Parameters

is

-

reference to input stream

Return value

is (reference to the stream after extraction of consecutive whitespace)

Notes

If eofbit is set on the stream prior to the call, the construction of the sentry object will set failbit.

Example

Run this code

#include <iostream>
#include <iomanip>
#include <istream>
#include <sstream>
#include <string>
 
int main()
{
    for (const char* str: {"     #1 test", "\t #2 test", "#3 test"})
    {
        std::string line;
        std::getline(std::istringstream{str}, line);
        std::cout << "getline returns:\t" << quoted(line) << '\n';
 
        std::istringstream iss{str};
        std::getline(iss >> std::ws, line);
        std::cout << "ws + getline returns:\t" << quoted(line) << '\n';
    }
}

Output:

getline returns:	"     #1 test"
ws + getline returns:	"#1 test"
getline returns:	"	 #2 test"
ws + getline returns:	"#2 test"
getline returns:	"#3 test"
ws + getline returns:	"#3 test"

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 415	C++98	calling std::ws might not construct the sentry object (insonsistent with other input functions)	required to construct the sentry object

See also

ignore

extracts and discards characters until the given character is found (public member function of std::basic_istream<CharT,Traits>)