Turbo C and ^Z's
Otto J. Makela
otto at tukki.jyu.fi
Mon Jan 7 17:08:56 AEST 1991
In article <1991Jan04.173903.20643 at dirtydog.ima.isc.com> karl at ima.isc.com (Karl Heuer) writes:
[...]
Lars is correct. On a file opened in append-mode, fseek() is only useful
for reading. (Though some historical implementations implemented append-
mode with an initial seek-to-end only, this is not acceptable in ANSI C.)
Yes. Confirm. Affirmative. Now that I've gone thru it, this seems to be
how it works. I didn't realize ANSI decided to break compatibility with Unix
in such a radical way...
>I'd like to point out I can't use "r+b", 'cause it'll fail if the file does
>not exist beforehand.
Then use "w+b".
Can't do that either, 'cause I don't want to kill the file. I need both.
Here is the fixed code, if someone finds it useful...
--
#include <stdio.h>
#include <fcntl.h>
#ifdef UNIX
#define fopena(filename) fopen(filename,"a")
#else
/*
** MeSsy-DOS kludge to replace fopen(filename,"at")
*/
FILE *fopena(filename)
char *filename; {
FILE *f;
if(f=fopen(filename,"r+b")) {
fseek(f,-1L,SEEK_END);
while(fgetc(f)==0x1A) fseek(f,-2L,SEEK_CUR);
/* This is needed to clear stdio buffering */
fseek(f,ftell(f),SEEK_SET);
setmode(fileno(f),O_TEXT);
} else
f=fopen(filename,"wt");
return f;
}
#endif
/*
** Test main program
*/
main(argc,argv)
int argc;
char *argv[]; {
FILE *f;
if(argc<2)
fprintf(stderr,"usage: %s file_to_append_to\n",*argv);
else if(f=fopena(argv[1])) {
fprintf(f,"This is the appended text.\n");
fclose(f);
} else
fprintf(stderr,"%s: could not open %s for append\n",
*argv,argv[1]);
}
--
/* * * Otto J. Makela <otto at jyu.fi> * * * * * * * * * * * * * * * * * * */
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