You are looking for getmntentother feature families *mntent. See manpage for further reference.
Sample code taken from here and slightly modified. /etc/mtabis a file containing a list of mounted file systems.
mounts = setmntent("/etc/mtab", "r");
while ( (ent = getmntent(mounts)) != NULL ){
if (strcmp(ent->mnt_type, "iso9660") == 0)
strcpy(retval[cd_count - 1], ent->mnt_dir);
}
}
endmntent(mounts);
, POSIX. glibc, , , /proc.