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Top Forums Programming how to move file pointer to a particular line in c Post 302178580 by ramkrix on Wednesday 26th of March 2008 12:22:54 AM
Old 03-26-2008
Hi,

I beleive you can do it with fseek itself by mentioning the bytes. See our terminal is 23*79, I mean to say 23 rows and 79 columns.

Say, if we have each coulmn occupies 1 character exactly, it means 1 byte. Therefore, a line can have 79 bytes of data in it. Then to move the nth line, you can use this formula
byte position=(((n-1)*number of bytes per line)+1).
I derived this formula, hope it will work.

Put this byte position in your fseek() function.

Please find the number of characters or bytes occpied by each column in a line of terminal. ere I assumed each column occupies 1 charcter and derived the formula.

please revert me back with the solution resulted.

regards,
Ramkrix
 

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PR(1)							    BSD General Commands Manual 						     PR(1)

NAME
pr -- print files SYNOPSIS
pr [+page] [-column] [-adFfmprt] [[-e] [char] [gap]] [-L locale] [-h header] [[-i] [char] [gap]] [-l lines] [-o offset] [[-s] [char]] [[-n] [char] [width]] [-w width] [-] [file ...] DESCRIPTION
The pr utility is a printing and pagination filter for text files. When multiple input files are specified, each is read, formatted, and written to standard output. By default, the input is separated into 66-line pages, each with o A 5-line header with the page number, date, time, and the pathname of the file. o A 5-line trailer consisting of blank lines. If standard output is associated with a terminal, diagnostic messages are suppressed until the pr utility has completed processing. When multiple column output is specified, text columns are of equal width. By default text columns are separated by at least one <blank>. Input lines that do not fit into a text column are truncated. Lines are not truncated under single column output. OPTIONS
In the following option descriptions, column, lines, offset, page, and width are positive decimal integers and gap is a nonnegative decimal integer. +page Begin output at page number page of the formatted input. -column Produce output that is columns wide (default is 1) that is written vertically down each column in the order in which the text is received from the input file. The options -e and -i are assumed. This option should not be used with -m. When used with -t, the min- imum number of lines is used to display the output. (To columnify and reshape text files more generally and without additional format- ting, see the rs(1) utility.) -a Modify the effect of the -column option so that the columns are filled across the page in a round-robin order (e.g., when column is 2, the first input line heads column 1, the second heads column 2, the third is the second line in column 1, etc.). This option requires the use of the -column option. -d Produce output that is double spaced. An extra <newline> character is output following every <newline> found in the input. -e [char][gap] Expand each input <tab> to the next greater column position specified by the formula n*gap+1, where n is an integer > 0. If gap is zero or is omitted the default is 8. All <tab> characters in the input are expanded into the appropriate number of <space>s. If any nondigit character, char, is specified, it is used as the input tab character. -F Use a <form-feed> character for new pages, instead of the default behavior that uses a sequence of <newline> characters. -f Same as -F but pause before beginning the first page if standard output is a terminal. -h header Use the string header to replace the file name in the header line. -i [char][gap] In output, replace multiple <space>s with <tab>s whenever two or more adjacent <space>s reach column positions gap+1, 2*gap+1, etc. If gap is zero or omitted, default <tab> settings at every eighth column position is used. If any nondigit character, char, is specified, it is used as the output <tab> character. -L locale Use locale specified as argument instead of one found in environment. Use "C" to reset locale to default. -l lines Override the 66 line default and reset the page length to lines. If lines is not greater than the sum of both the header and trailer depths (in lines), the pr utility suppresses output of both the header and trailer, as if the -t option were in effect. -m Merge the contents of multiple files. One line from each file specified by a file operand is written side by side into text columns of equal fixed widths, in terms of the number of column positions. The number of text columns depends on the number of file operands suc- cessfully opened. The maximum number of files merged depends on page width and the per process open file limit. The options -e and -i are assumed. -n [char][width] Provide width digit line numbering. The default for width, if not specified, is 5. The number occupies the first width column posi- tions of each text column or each line of -m output. If char (any nondigit character) is given, it is appended to the line number to separate it from whatever follows. The default for char is a <tab>. Line numbers longer than width columns are truncated. -o offset Each line of output is preceded by offset <spaces>s. If the -o option is not specified, the default is zero. The space taken is in addition to the output line width. -p Pause before each page if the standard output is a terminal. pr will write an alert character to standard error and wait for a car- riage return to be read on the terminal. -r Write no diagnostic reports on failure to open a file. -s char Separate text columns by the single character char instead of by the appropriate number of <space>s (default for char is the <tab> character). -t Print neither the five-line identifying header nor the five-line trailer usually supplied for each page. Quit printing after the last line of each file without spacing to the end of the page. -w width Set the width of the line to width column positions for multiple text-column output only. If the -w option is not specified and the -s option is not specified, the default width is 72. If the -w option is not specified and the -s option is specified, the default width is 512. file A pathname of a file to be printed. If no file operands are specified, or if a file operand is '-', the standard input is used. The standard input is used only if no file operands are specified, or if a file operand is '-'. The -s option does not allow the option letter to be separated from its argument, and the options -e, -i, and -n require that both arguments, if present, not be separated from the option letter. ERRORS
If pr receives an interrupt while printing to a terminal, it flushes all accumulated error messages to the screen before terminating. DIAGNOSTICS
The pr utility exits 0 on success, and 1 if an error occurs. Error messages are written to standard error during the printing process (if output is redirected) or after all successful file printing is complete (when printing to a terminal). SEE ALSO
cat(1), more(1), rs(1) STANDARDS
The pr utility is IEEE Std 1003.1-2001 (``POSIX.1'') compatible. HISTORY
A pr command appeared in Version 1 AT&T UNIX. BSD
September 20, 2001 BSD
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