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Top Forums Programming how to move file pointer to a particular line in c Post 302178615 by ramkrix on Wednesday 26th of March 2008 03:01:35 AM
Old 03-26-2008
CPU & Memory

Quote:
char data[80];
long cur_pos;
while( feof(fh) == 0){
cur_pos = ftell(fh);
printf( "cur_cursor = %ld \n", cur_pos);
fgets(data, 80, fh);
}
A simple change to this code may work:

char data[80];
int ct_str_length;
long new_byte_position;

long cur_pos;
while( feof(fh) == 0){
cur_pos = ftell(fh);
printf( "cur_cursor = %ld \n", cur_pos);
fgets(data, 80, fh);
ct_str_length=strlen(data);
new_byte_position=ct_str_length+1;
printf("new_byte_position or cursor position is %ld" ,new_byte_position);
fseek(fh,new_byte_position,SEEKSET);

}



we know that fgets() stops once it reaches newline characte/EOF.

Till EO of file is reached(feof(fp)==0), with the curent byte position as 0th byte or first byte of first line, we are reading the first line by fgets() till newline characte is reached. Once \n is reached, fgets() tops its function and the ead content is stored in data array. the string length in this aray is the total number of characters/bytes in first line. So adding 1 byte more than that, now the current byte position becomes the beginning byte of the next line. Check this.

-Ramkrix
 

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gets(3C)						   Standard C Library Functions 						  gets(3C)

NAME
gets, fgets - get a string from a stream SYNOPSIS
#include <stdio.h> char *gets(char *s); char *fgets(char *s, int n, FILE *stream); DESCRIPTION
The gets() function reads bytes from the standard input stream (see Intro(3)), stdin, into the array pointed to by s, until a newline char- acter is read or an end-of-file condition is encountered. The newline character is discarded and the string is terminated with a null byte. If the length of an input line exceeds the size of s, indeterminate behavior may result. For this reason, it is strongly recommended that gets() be avoided in favor of fgets(). The fgets() function reads bytes from the stream into the array pointed to by s, until n-1 bytes are read, or a newline character is read and transferred to s, or an end-of-file condition is encountered. The string is then terminated with a null byte. The fgets() and gets() functions may mark the st_atime field of the file associated with stream for update. The st_atime field will be marked for update by the first successful execution of fgetc(3C), fgets(), fread(3C), fscanf(3C), getc(3C), getchar(3C), gets(), or scanf(3C) using stream that returns data not supplied by a prior call to ungetc(3C) or ungetwc(3C). RETURN VALUES
If end-of-file is encountered and no bytes have been read, no bytes are transferred to s and a null pointer is returned. For standard-con- forming (see standards(5)) applications, if the end-of-file indicator for the stream is set, no bytes are transferred to s and a null pointer is returned whether or not the stream is at end-of-file. If a read error occurs, such as trying to use these functions on a file that has not been opened for reading, a null pointer is returned and the error indicator for the stream is set. If end-of-file is encoun- tered, the EOF indicator for the stream is set. Otherwise s is returned. ERRORS
Refer to fgetc(3C). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
lseek(2), read(2), ferror(3C), fgetc(3C), fgetwc(3C), fopen(3C), fread(3C), getchar(3C), scanf(3C), stdio(3C), ungetc(3C), ungetwc(3C), attributes(5), standards(5) SunOS 5.11 15 Oct 2003 gets(3C)
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