istream& seekg ( streampos pos );
istream& seekg ( streamoff off, ios_base::seekdir dir );
Set position of the get pointer
Sets the position of the get pointer.
The get pointer determines the next location to be read in the source associated to the stream.
Parameters
- pos
- The new position in the stream buffer. This parameter is an integral value of type streampos.
- off
- Integral value of type streamoff representing the offset to be applied relative to an absolute position specified in the dir parameter.
- dir
- Seeking direction. It is an object of type ios_base::seekdir that specifies an absolute position from where the offset parameter off is applied. It can take any of the following member constant values:
| value | offset is relative to... |
|---|
| ios_base::beg | beginning of the stream buffer |
| ios_base::cur | current position in the stream buffer |
| ios_base::end | end of the stream buffer |
Return Value
The function returns *this.
Errors are signaled by modifying the internal state flags:
| flag | error |
|---|
| eofbit | - |
| failbit | The parameter(s) describe a position that could not be reached. |
| badbit | An error other than the above happened. |
Additionally, in any of these cases, if the appropriate flag has been set with member function ios::exceptions, an exception of type ios_base::failure is thrown.
Example
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// load a file into memory
#include <iostream>
#include <fstream>
using namespace std;
int main () {
int length;
char * buffer;
ifstream is;
is.open ("test.txt", ios::binary );
// get length of file:
is.seekg (0, ios::end);
length = is.tellg();
is.seekg (0, ios::beg);
// allocate memory:
buffer = new char [length];
// read data as a block:
is.read (buffer,length);
is.close();
cout.write (buffer,length);
delete[] buffer;
return 0;
}
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In this example seekg is used to move the get pointer to the end of the file, and then back to the beginning.
Basic template member declaration
( basic_istream<charT,traits> )
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typedef traits::pos_type pos_type;
typedef traits::off_type off_type;
basic_istream<charT,traits> & seekg ( pos_type pos );
basic_istream<charT,traits> & seekg ( off_type off, ios_base::seekdir dir );
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See also
| istream::tellg | Get position of the get pointer. (public member function) |
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