|
hi,
Can you say something more about fseek please?
how to use fseek to go to a certain line of a file.
For examlpe, I need to overwrite the thrid line of the file.
But fseek and fgetpos simply moving the file pointer in the same line, not be able to next line.
Thankx.
chauteen
|
|
|
|
|
doesn't fscanf read the "\t", "\n" characters? if so. read the entire file in CString and handle the CString.
(you can always google, Codeguru, codeproject on tutorials and examples.)
info on fseek from MSDN:
Run-Time Library Reference
fseekSee Also
Stream I/O Routines | ftell | _lseek | rewind | Run-Time Routines and .NET Framework Equivalents
Requirements
Function Required header Compatibility
fseek <stdio.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP
For additional compatibility information, see Compatibility in the Introduction.
Libraries
All versions of the C run-time libraries.
Moves the file pointer to a specified location.
int fseek(
FILE *stream,
long offset,
int origin
);
Parameters
stream
Pointer to FILE structure.
offset
Number of bytes from origin.
origin
Initial position.
Return Value
If successful, fseek returns 0. Otherwise, it returns a nonzero value. On devices incapable of seeking, the return value is undefined.
Remarks
The fseek function moves the file pointer (if any) associated with stream to a new location that is offset bytes from origin. The next operation on the stream takes place at the new location. On a stream open for update, the next operation can be either a read or a write. The argument origin must be one of the following constants, defined in STDIO.H:
SEEK_CUR
Current position of file pointer.
SEEK_END
End of file.
SEEK_SET
Beginning of file.
You can use fseek to reposition the pointer anywhere in a file. The pointer can also be positioned beyond the end of the file. fseek clears the end-of-file indicator and negates the effect of any prior ungetc calls against stream.
When a file is opened for appending data, the current file position is determined by the last I/O operation, not by where the next write would occur. If no I/O operation has yet occurred on a file opened for appending, the file position is the start of the file.
For streams opened in text mode, fseek has limited use, because carriage return–linefeed translations can cause fseek to produce unexpected results. The only fseek operations guaranteed to work on streams opened in text mode are:
Seeking with an offset of 0 relative to any of the origin values.
Seeking from the beginning of the file with an offset value returned from a call to ftell.
Also in text mode, CTRL+Z is interpreted as an end-of-file character on input. In files opened for reading/writing, fopen and all related routines check for a CTRL+Z at the end of the file and remove it if possible. This is done because using fseek and ftell to move within a file that ends with a CTRL+Z may cause fseek to behave improperly near the end of the file.
Requirements
Function Required header Compatibility
fseek <stdio.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP
For additional compatibility information, see Compatibility in the Introduction.
Libraries
All versions of the C run-time libraries.
Example
// crt_fseek.c
/* This program opens the file FSEEK.OUT and
* moves the pointer to the file's beginning.
*/
#include <stdio.h>
int main( void )
{
FILE *stream;
char line[81];
int result;
stream = fopen( "fseek.out", "w+" );
if( stream == NULL )
printf( "The file fseek.out was not opened\n" );
else
{
fprintf( stream, "The fseek begins here: "
"This is the file 'fseek.out'.\n" );
result = fseek( stream, 23L, SEEK_SET);
if( result )
perror( "Fseek failed" );
else
{
printf( "File pointer is set to middle of first line.\n" );
fgets( line, 80, stream );
printf( "%s", line );
}
fclose( stream );
}
}
Output
File pointer is set to middle of first line.
This is the file 'fseek.out'.
See Also
Stream I/O Routines | ftell | _lseek | rewind | Run-Time Routines and .NET Framework Equivalents
--------------------------------------------------------------------------------
Send feedback on this topic to Microsoft
© Microsoft Corporation. All rights reserved.
"If I don't see you in this world, I'll see you in the next one... and don't be late." ~ Jimi Hendrix
|
|
|
|
|
Thanks for your reply first.
For I am trying your way, to read the entire file and then write the whole data back.(the work I want to do is store 8 spin vlaue to a file, and update when the user click and change spin value.)
but I use a brute force way, for I don't know how to read data in CString
I declare an BYTE array, called buffer[8], and in the dialog's init, I read in the file
fread( buffer, sizeof( BYTE ), 8, filespin );
and in the spin message, I add
<br />
fseek(filespin, 0, SEEK_SET);<br />
fprintf( filespin, "%s", buffer );<br />
I've also tried fwrite
<br />
fwrite( buffer, sizeof( BYTE ), 8, filespin );<br />
both failed
the output file will contain some strange code, like slash , camma or something.
I try to show the readin buffer text on a editbox, and it already contain a unexpected slash and the end.
It seems the read in have something wrong already, not to mention write data back.
Can you suggest me some smart or "correct" way to do?
Thank you very much.
chauteen
|
|
|
|
|
I suppose you are using MFC? Then you know that a spinbutton is a textbox attached with a spincontrol.
Get a handle to your textboxes (assign a control variable or via GetDlgItem)
eg your handlers are called: edit1, edit2, ... edit8
and assign CStrings eg. string1 -> string8
then you can do when onchangeedit1 occurs.
edit1.GetWindowText(string1);
etc...
then print them with fprintf and read them with freadf.
If you don't use CString use char or a char array, not BYTE. (a BYTE can be anything).
You could try casting the BYTE to a char, but I'm not sure what it will give.
I think the reason of your strange results is that a BYTE will not be interpreted as a character, but that just a guess.
if the char array doesn't seem to work you probably forgot the "\o" character.
You can find this stuff on MSDN. Look on CString, GetWindowText (SetWindowText) etc.
(note: if you can't assign a control variable do this:
CWnd* pWnd;<br />
pWnd = (CWnd*)GetDlgItem(IDC_NAMEOF_EDIT_BOX);<br />
pWnd->GetWindowText(.....) .... )
"If I don't see you in this world, I'll see you in the next one... and don't be late." ~ Jimi Hendrix
|
|
|
|
|
First thanks for your help.
Right now, I use GetWindowText to get the edit box text, and over write the "whole" data at every onchangeedit message.(Still a kind of lazy;P) Any way it works.
I'm wondering if the situation happened with reading and modifyind large file. how could one read out the whole data, and write it back at every edit change just because not be able to use fseek to move the file pointer to a certain "line". (for fprint can only move the file pointer to certain "byte " from origin)
chauteen
|
|
|
|
|
What we do here at work is to add "metadata" in the file, but still we always read the entire file into CStrings.
You can do something like:
"#value1|value2|...|valuen#" Where # = beginning - end and the | is a delimiter.
Note that 1 character is 1 byte long, this means you can load about 13000 lines (1 line ~ 80 characters) for each MegaByte of memory. Normally you have about 512 Mb, not to mention virtual memory.
Point is, it's really no problem loading the file into memory. The reading takes time, but as you may have noticed, Word, Excel, Notepad, ... all take some time to load their text.
"If I don't see you in this world, I'll see you in the next one... and don't be late." ~ Jimi Hendrix
|
|
|
|
|
hi V.
I'm sorry keeping on bothering you.
I agree with you, it is ok to load the whole data to memory.
But I need to write data back and close the file at every editchange, because the file will be accessed by another class.
Fortunately, I have only 8 data need to handle, the speed is compltely fine with me.
My tesk is like this:
I use MFC to make a dialog.
I have serveral tabs with about 8 spins on each of them. and I add these tabs on a base dailog.
I send the spin value out on a master query(I'm slave on the bus. I cann't send data out on my own. I need to wait the query command.)
So I decide to store the tabs spin values in several files(every tab has it's own file), and open a serial port on the base port.
When the user change the spin value, he only change the file, but doesn't send it out.
When the master polling, I send the file data to master.(the polling speed is faster than the user's finger to click spin, of course)
Will my idea work?
One more ask
V. wrote:
"#value1|value2|...|valuen#"
if I make my file like this:
10
15
20
when I fread them, CString will treat 10 to be one byte, or treat 1 as one byte and 0 as teh second byte?
Many thanks for your help beforehan.
slow-witted chauteen
|
|
|
|
|
Well actually it depends on which coding you use, but 90% of all uses are ASCII which (in modern times) takes 1 byte per character. A character is not only a, b, c, ... or 0-9, but also a space, tab, return ,...
so 10 would be 2 bytes. (a byte stands for BY EIGHT, 8 bits) (and 1 byte for return and I even think 1 byte for the new line, but I'm not sure the fread will read them)
For your idea, yes it will work I think, but I would consider putting them in 1 file, this is however just a detail.
My experience is that the boss will not tire himself too much by checking how you did it, he just wants it working (no matter what dirty tricks  )
good luck.
"If I don't see you in this world, I'll see you in the next one... and don't be late." ~ Jimi Hendrix
|
|
|
|
|
Are there good WMI samples, articles, books ?
I need to work with system objects, like users and directories...
So need any links and names.
Language C++,
but others is interesting also.
Thanks you.
|
|
|
|
|
There are quite a few samples / articles on this site. Type WMI into the search and go from there. 
Ant.
I'm hard, yet soft.
I'm coloured, yet clear.
I'm fuity and sweet.
I'm jelly, what am I? - David Williams (Little Britain)
|
|
|
|
|
Hello,
I'm working at a machine where where the VC++ batch file for setting the PATH environment variables isn't available and I don't have access to the CD today. Can anybody remind me exactly what variables are set?
Cheers,
John
p.s.
or even just paste the script would be brilliant!
|
|
|
|
|
The file vcvars32.bat, located in the C:\Program Files\Microsoft Visual Studio\VC98\Bin folder, looks like:
@echo off
rem
rem Root of Visual Developer Studio Common files.
set VSCommonDir=C:\Program Files\MICROS~3\Common
rem
rem Root of Visual Developer Studio installed files.
rem
set MSDevDir=C:\Program Files\MICROS~3\Common\msdev98
rem
rem Root of Visual C++ installed files.
rem
set MSVCDir=C:\Program Files\MICROS~3\VC98
rem
rem VcOsDir is used to help create either a Windows 95 or Windows NT specific path.
rem
set VcOsDir=WIN95
if "%OS%" == "Windows_NT" set VcOsDir=WINNT
rem
echo Setting environment for using Microsoft Visual C++ tools.
rem
if "%OS%" == "Windows_NT" set PATH=%MSDevDir%\BIN;%MSVCDir%\BIN;%VSCommonDir%\TOOLS\%VcOsDir%;%VSCommonDir%\TOOLS;%PATH%
if "%OS%" == "" set PATH="%MSDevDir%\BIN";"%MSVCDir%\BIN";"%VSCommonDir%\TOOLS\%VcOsDir%";"%VSCommonDir%\TOOLS";"%windir%\SYSTEM";"%PATH%"
set INCLUDE=%MSVCDir%\ATL\INCLUDE;%MSVCDir%\INCLUDE;%MSVCDir%\MFC\INCLUDE;%INCLUDE%
set LIB=%MSVCDir%\LIB;%MSVCDir%\MFC\LIB;%LIB%
set VcOsDir=
set VSCommonDir=
"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen
|
|
|
|
|
Thanks very much David,
John
|
|
|
|
|
I have a data file which was written in a text ascii format, I would like to generate a report, describe the filename, date, etc, also extract some data and presented them in a curve, the data should also be listed in a table.
I was used doc/view to realize it, but it looks not very fancy, especially I have to draw the table line by line. Any good idea?
Thanks.
Nelson L.
|
|
|
|
|
Create an MDI project and instead of drawing your own table, try Codeproject's own MFCGrid in one of the views. It's quite easy to use IMO.
John
|
|
|
|
|
how to use them
my problem is as follow
i hav got a matrix ,the user wil enetr the value in the matrix & i hav 2 pic the value from txtboxes.
I Think It will Work
Alok Gupta
visit me at http://www.thisisalok.tk
|
|
|
|
|
ON_COMMAND_RANGE is used when you want to call the same function for several buttons or events.
I don't understand what you want to do ??
|
|
|
|
|
Hello:
I am writting a Date Class, and I want to overload operator - that can take a Date object, I wrote the code, but I felt it is stupid, Please help me:
***************************************************************************
int Date::days[] = {0, 31, 28, 31, 30, 31, 30,
31, 31, 30, 31, 30, 31};
int Isbigger(int year, int right_year)
{
int bigger;
bigger = year > right_year?year:right_year;
returen bigger;
}//get the bigger value of two
int Issmaller(int year, int right_year)
{
int smaller;
smaller = year < right_year? year:right_year;
return smaller;
}//get the smaller value of two
int Date::operator -(Date right)
{
int subday;
int subyear;
if (year == right.year)
{
subyear = 0;
if(month == right.month)
{
subday = Isbigger(day, right.day) - Issmaller(day,right.day); //if the same year and same month, just subtract the date;
}
else if(month != right.month) //if same year different month,
{
subday = (days[month] - day) + right.day); //get the days in beginning and ending month,
for(i = (Isbigger(day,right.day) - 1); i >issmaller(day,right.day) ; i++)
{
subday += days[i]; //then plus the intermedia month,
}
}
}
else //not in the same year
{
int yearDifference;
yearDifference = Isbigger(year,right.year) - 1;
subyear = yearDifference * 365;
if(month == right.month)
{
subday = Isbigger(day, right.day) - Issmaller(day,right.day); //if the same year and same month, just subtract the date;
}
else if(month != right.month) //if same year different month,
{
subday = (days[month] - day) + right.day); //get the days in beginning and ending month,
for(i = (Isbigger(day,right.day) - 1); i >issmaller(day,right.day) ; i++)
{
subday += days[i]; //then plus the intermedia month,
}
}
subday += subyear;
}
return subday;
}
Thank You So Much
|
|
|
|
|
In some programs they convert the date to a number. (eg. like CTime class) then you can detect real easy is bigger or smaller and just substract or add them.
I would take in account that in the year 2004 february has 29 days... leap years.
good luck.
"If I don't see you in this world, I'll see you in the next one... and don't be late." ~ Jimmy Hendrix
|
|
|
|
|
Hello,
Think it goes something like this, but you should check on web ...
if year is divisible by 4 then
....if year is not divisible by 100 then
.........it's a leap year
....else
.........if year is divisible by 400 then
...............it's a leap year
.........endif
....endif
endif
John
|
|
|
|
|
Hello,
This mightn't be exactly what your asking but you should make the '-' operator a 'friend' rather than a class member. It means you can use it like the built-in subtraction operator instead of call a method.
See http://guinness.cs.stevens-tech.edu/~asatya/courses/cs765IT/C++_overview/lect10_1.pdf
John
|
|
|
|
|
Hello,
my MFC dialog based app uses a freeware activex I found on the net.
To use it, the relative ocx file must be registered in the system.
Is there a way to make the app do itself without the user having
to run regsvr32 c:\..... ?
i.e. to register at execution and unregister on close app?
Thanks for the precious help.
Marco.
|
|
|
|
|
Does ALU inside the cpu handle floating point?
or cpu will let the FPU handle it? For example,
when we declare float, or double?
Another newbie's question:
When we do assambly language, we will specify
which register to use, so my question is: do
we need to have to specify when to use cache?
or the cpu will just simply decide when to use
cache itself?
|
|
|
|
|
Is my question too dump? seriously
|
|
|
|
|
Hello everyone!
I'm not quite sure, if this is the correct message board for this thread, but i'm working with C++ so I posted this thread here.
I've created an Win32 Application, which checks if the .net Framework is installed on the system. If not, the program will automatically start to install the .net Framework in the background.
Is there any way to run a Windows Installer Package in the background (command line, etc.)??
For example I have myinstaller.msi or dotnetfx.exe!
How can I solve my problem???
Thank you for helping me!
|
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
