c - Can't use lseek to add a space at the end of a file -

i trying append text opened file. i'd append pid number @ end of file. example: lorem ipsum dolor sit amet orci aliquam. 14872. code works fine except failing @ making program print space between last character of file , first digit of pid. i've tried use lseek() adding 1 offset end of file and, said, failed miseably. don't understand what's wrong, because apparently getting expected results:

buffer size: 5. buffer content: 14872. current position: 41. 

and output:

lorem ipsum dolor sit amet orci aliquam.14872 

which makes no sense me. here code:

void writeintheend(const int fd, const int pid, const int base) {     char *buffer;     int buffer_size = getcharsfromint(pid, base);     printf("buffer size: %d.\n", buffer_size);     buffer = (char *) malloc (sizeof(char) * buffer_size);     sprintf(buffer, "%d", pid);     printf("buffer content: %s.\n", buffer);      //it should add space , write pid     lseek(fd, 1, seek_end);     printf("current position: %d.\n", lseek(fd, 0, seek_cur));     write(fd, buffer, buffer_size);     free(buffer); } 

seeking off end of file doesn't pad spaces leaves null bytes until written gap. you'll need write leading ' ' pid buffer write end (without seek past end of file).