this is for an assignment (not mine, but someone I'm helping, if that matters), but were supposed to write a program that mimics the unix ar command. I am very close to writing the file info to the header, using the stat() function, but I'm getting @^ instead of spaces when writing to the file.
here is an example of output
1-s.txt2^@^@^@^@^@^@^@^@Wed Oct 30 149972^@14601^@100640^@^@101^@^@^@^@^@^@^@
and it should be
1-s.txt2/ Wed Oct 30 149972 14601 100640 101
except the date should be a unix timestamp, any help with that would also be appreciated.
Thanks!!!
struct ar_hdr headerstruct;
void setfileinfo(const struct stat *sfileinfo){
sprintf(headerstruct.ar_name, "%s", global_argv[3]);
sprintf(headerstruct.ar_date, "%s", ctime(&sfileinfo->st_mtime));
sprintf(headerstruct.ar_uid, "%ld", (long)sfileinfo->st_uid);
sprintf(headerstruct.ar_gid, "%ld", (long) sfileinfo->st_gid);
sprintf(headerstruct.ar_mode, "%lo",(unsigned long)sfileinfo->st_mode);
sprintf(headerstruct.ar_size, "%lld",(long long)sfileinfo->st_size);
char filemag[2] = "`\n";
int fd;
fd = open(global_argv[2], O_RDWR);
lseek(fd, 0, SEEK_END);
write(fd, headerstruct.ar_name, 16);
write(fd, headerstruct.ar_date, 12);
write(fd, headerstruct.ar_uid, 6);
write(fd, headerstruct.ar_gid, 6);
write(fd, headerstruct.ar_mode, 8);
write(fd, headerstruct.ar_size, 10);
write(fd, filemag ,2);
return;
}
Since the ar header requires space padding, you might consider using memset to prefill the data structure or specific members with spaces. For example:
memset(&headerstruct, ' ', sizeof(headerstruct));
Additionally, if you want to avoid null-terminated strings in the header, you should use something like memcpy or strncpy (with an appropriate length) instead of sprintf, as sprintf will insert a zero byte at the end of the string.