toton wrote:
Quote:
On Feb 15, 12:30 pm, John Harrison <john_androni...@hotmail.com>
wrote:
>
Quote:
>>toton wrote:
>>
Quote:
>>>Hi,
>> I want to unread a few things while I am reading a file. One
>>>solution I know is putback the characters read to the buffer.
>> But as I need frequent moving file pointer , to a few steps back, I
>>>was thinking of seekg & tellg function. But it is not workings as I
>>>expect....
>>
Quote:
>>>here is the test code,
>>>std::string word;
>>>std::string value;
>>>while(stream_){
>> std::ifstream::pos_type pos = stream_.tellg();///Mark the current
>>>stream pos (2933)
>> stream_ >word; ///read the word
>> std::ifstream::pos_type pos1 = stream_.tellg();///stream pos (2942)
>>>good
>> if(word == ".PEN_DOWN"){
>> int y;
>> stream_>>y; /// read some int from stream (the next one was int here
>>>209, thus successful).
>> stream_.seekg(pos); ///seek to previous pos i.e 2933
>> std::ifstream::pos_type pos2 = stream_.tellg();///once again
>>>check the current pos. Yes it is 2933
>> std::string x;
>> stream_>>x;///now read the string I expect it to be .PEN_DOWN
>>>again. but it is 198 :(
>>>}
>>>The content of the file at that portion is,
>>
Quote:
>>>.SEGMENT WORD 0-5 OK "Zaadje"
>>>.PEN_DOWN
>>209 1810
>>198 1812
>>198 1812
>>198 1813
>>
Quote:
>>Is this a problem with internal buffering or operator>? How can
>>>otherwise I go to the previously marked position ?
>>
>>
>>I compiled your code and it worked for me. Either you have a bug in your
>>version of the STL or (much more likely) a bug somewhere else in your
>>code. Why not post a complete (and hopefully small) program that
>>illustrates this problem and someone will take a look.
>>
>>john
>
>
I checked it. It is working fine with some ascii file . But not
working with a file, which I belief is utf-8 / contains \n\r as new
line char or some other problem (Which In windows notepad shows some
unknown char for newline and makes a horrible display, shows fine in
gvim)
Again this works if I manually feed a few lines with strstream.
so may be the getline function, which I used in a few places creates
the problem. Not sure how to make it work with a \n or \r or both.
Using VS2003 .NET (7.1)
>
There's a few possibilities here
1) Don't mix getline with operator>>, it only causes problems. The
problem being that it's hard to be sure whether operator>does or
doesn't read the end of line, which has a big effect on how the next
getline operates.
2) Understand binary mode
http://www.parashift.com/c++-faq-lit...html#faq-15.12
3) getline takes an optional third parameter, which is the end of line
character
getline(in_file, line, '#')
reads a 'line' using # as an end of line character.
That said if you are really reading utf-8 then I expect you'll end up
writing your own I/O routines that use binary mode and read the input
one byte at a time.
john
