std::basic_istream::seekg

 

C++

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Technical Specifications

 

Input/output library

I/O manipulators

C-style I/O

Buffers

basic_streambuf

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basic_istream

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basic_stringstream

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istrstream (deprecated in C++98)

ostrstream (deprecated in C++98)

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Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

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fpos

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iostream_category (C++11)

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std::basic_istream

Global objects

cinwcin

Member functions

basic_istream::basic_istream

basic_istream::~basic_istream

basic_istream::operator= (C++11)

Formatted input

basic_istream::operator>>

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basic_istream::get

basic_istream::peek

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basic_istream::getline

basic_istream::ignore

basic_istream::read

basic_istream::readsome

basic_istream::gcount

Positioning

basic_istream::tellg

basic_istream::seekg

Miscellaneous

basic_istream::sync

basic_istream::swap (C++11)

Member classes

basic_istream::sentry

Non-member functions

operator>>(std::basic_istream)

 

basic_istream& seekg( pos_type pos );
basic_istream& seekg( off_type off, std::ios_base::seekdir dir);

Sets input position indicator of the current associated streambuf object. In case of failure, calls setstate(std::ios_base::failbit).

Before doing anything else, seekg clears eofbit.

(since C++11)

seekg behaves as UnformattedInputFunction, except that gcount() is not affected. After constructing and checking the sentry object,

1) sets the input position indicator to absolute (relative to the beginning of the file) value pos. Specifically, executes rdbuf()->pubseekpos(pos, std::ios_base::in).

2) sets the input position indicator to position off, relative to position, defined by dir. Specifically, executes rdbuf()->pubseekoff(off, dir, std::ios_base::in).

Parameters

pos	-	absolute position to set the input position indicator to.
off	-	relative position to set the input position indicator to.
dir	-	defines base position to apply the relative offset to. It can be one of the following constants: Constant Explanation beg the beginning of a stream end the ending of a stream cur the current position of stream position indicator

Return value

*this

Exceptions

failure if an error occurred (the error state flag is not goodbit) and exceptions() is set to throw for that state.

If an internal operation throws an exception, it is caught and badbit is set. If exceptions() is set for badbit, the exception is rethrown.

Example

Run this code

#include <iostream>
#include <string>
#include <sstream>
 
int main()
{
    std::string str = "Hello, world";
    std::istringstream in(str);
    std::string word1, word2;
 
    in >> word1;
    in.seekg(0); // rewind
    in >> word2;
 
    std::cout << "word1 = " << word1 << '\n'
              << "word2 = " << word2 << '\n';
}

Output:

word1 = Hello,
word2 = Hello,

See also

tellg	returns the input position indicator (public member function)
tellp	returns the output position indicator (public member function of std::basic_ostream)
seekp	sets the output position indicator (public member function of std::basic_ostream)