I have to delete the whole line in the file (first word matches), how can I ?

[santa19992000]

I have a file called xyz.txt, if the first word matches, I have to
delete the whole line, how can I do that. sample is below

file xyz.txt
=======
SP 0/23/2345/345
CL 00/34/3456/54

In the above file, if the first word "SP" matches, then I have to
delete the whole line in that file, How to delete. Thanks.

[Keith Thompson]

sa***********@yahoo.com writes:

I have a file called xyz.txt, if the first word matches, I have to
delete the whole line, how can I do that. sample is below

file xyz.txt
=======
SP 0/23/2345/345
CL 00/34/3456/54

In the above file, if the first word "SP" matches, then I have to
delete the whole line in that file, How to delete. Thanks.

You can't really delete a line from a file. What you can do is create
a new file containing everything except the line that you don't want.
If you like, you can then rename the new file, replacing the original
one.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[slebetman]

sa***********@yahoo.com wrote:

I have a file called xyz.txt, if the first word matches, I have to
delete the whole line, how can I do that. sample is below

file xyz.txt
=======
SP 0/23/2345/345
CL 00/34/3456/54

In the above file, if the first word "SP" matches, then I have to
delete the whole line in that file, How to delete. Thanks.

The usual way of doing this, in pseudocode:

foreach line in FILE {
// only print out lines that does not begin with SP:
if ( ! beginsWith(line, "SP")) {
fprintf( TEMP, "%s", line );
}
}
// on most OS renaming replaces the old file:
rename( "TEMP", "FILE" );

[Christopher Benson-Manica]

Keith Thompson <ks***@mib.org> wrote:

You can't really delete a line from a file. What you can do is create
a new file containing everything except the line that you don't want.

Or come up with something foolish (as I did) such as the following...

#include <stdio.h>
#include <assert.h>
#include <string.h>

int main( void )
{
long int pos=0;
FILE *fp=fopen( "test.txt", "r+" );
char readbuf[256], storebuf[8<<10];
int found=0, bytecount=0;
assert( fp );
while( fgets(readbuf,sizeof readbuf,fp) ) {
if( strstr(readbuf,"test") ) {
bytecount+=strlen( readbuf );
found=1;
}
else if( !found ) {
pos=ftell( fp );
}
else {
strcat( storebuf, readbuf ); /* Assume storebuf is large enough */
}
}
if( pos ) {
fseek( fp, pos, SEEK_SET );
fputs( storebuf, fp );
}
while( bytecount-- > 0 ) {
fputc( 0, fp );
}
if( found ) {
fputc( "\n" );
}
fclose( fp );
return 0;
}

My thought was to alter the file to make it superficially appear that
the lines had been deleted. Is the last "line" of the file (a string
null characters followed by a newline) guaranteed to look like an
empty string to the next program that reads it with fgets()? I of
course don't present this as a good idea; I just thought it would be
fun to try.

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cyberspace.org | don't, I need to know. Flames welcome.

[Richard Heathfield]

Christopher Benson-Manica said:

Keith Thompson <ks***@mib.org> wrote:

You can't really delete a line from a file. What you can do is create
a new file containing everything except the line that you don't want.

Or come up with something foolish (as I did) such as the following...

#include <stdio.h>
#include <assert.h>
#include <string.h>

int main( void )
{
long int pos=0;
FILE *fp=fopen( "test.txt", "r+" );
char readbuf[256], storebuf[8<<10];
int found=0, bytecount=0;
assert( fp );

In C90, the behaviour of this assertion is undefined.

assert(fp != NULL);

is fine from a behaviour perspective. It's not fine, though, as an example
of good programming practice. A quick hack, presumably?

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Christopher Benson-Manica]

Richard Heathfield <in*****@invalid.invalid> wrote:

In C90, the behaviour of this assertion is undefined.
Does that mean I get to use the C99 escape hatch? :-)
is fine from a behaviour perspective. It's not fine, though, as an example
of good programming practice. A quick hack, presumably?

The whole program was really not a great idea from a programming
practice perspective, so yes, a quick hack indeed.

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cyberspace.org | don't, I need to know. Flames welcome.

[Richard Heathfield]

Christopher Benson-Manica said:

Richard Heathfield <in*****@invalid.invalid> wrote:

In C90, the behaviour of this assertion is undefined.

Does that mean I get to use the C99 escape hatch? :-)

Only if you implement one! :-)

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)