关于ifstream的简单问题

[dreadknight3]

怎样才能实现让ifstream流的文件指针往回移动一个字符?

[P6689]

istream::seekg(-1)

[jixingzhong]

seekg
Syntax:

#include <fstream>
istream& seekg( off_type offset, ios::seekdir origin );
istream& seekg( pos_type position );

The function seekg() is used with input streams, and it repositions the "get" pointer for the current stream to offset bytes away from origin, or places the "get" pointer at position.

[jixingzhong]

如果是 ofstream，
则使用这个：

seekp
Syntax:

#include <fstream>
ostream& seekp( off_type offset, ios::seekdir origin );
ostream& seekp( pos_type position );

The seekp() function is used with output streams, but is otherwise very similar to seekg().

[dreadknight3]

试过 istream::seekg(1)
是把文件指针移动到1这个绝对位置
如果我要把文件指针移动到当前指针下一个位置该怎样做？

[taodm]

用seekg／seekp的双参版本呀。

[jixingzhong]

Enumeration seekdir
Enumeration Position
beg Begging of stream
cur Current position of stream
end End of stream

第二个参数控制即可

[jixingzhong]

istream.seekg (1, ios::cur); //当前位置进行相对移动

[yuyunliuhen]

// basic_istream_seekg.cpp
// compile with: /EHsc
#include <iostream>
#include <fstream>

int main ( )
{
using namespace std;
ifstream file;
char c, c1;

file.open( "basic_istream_seekg.txt" );
file.seekg(2); // chars to skip
file >> c;
cout << c << endl;

file.seekg( 0, ios_base::beg );
file >> c;
cout << c << endl;

file.seekg( -1, ios_base::end );
file >> c1;
cout << c1 << endl;
}