Why is nothing printing from the text file? - c

Question

I was trying out some exercises with the C language, specifically open() and read(). However, I've reached an impasse when I try printing to STDOUT the contents of a a text file (text.txt) that I have in the same directory as the c file. The size in bytes get printed, but the contents of the file do not.
I allocated space according to the size of the file, and added "1" for the null terminator. The manual page for read() states that it reads the contents of the file into the second parameter (void* buff). What am I missing/doing wrong?
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int main(int argc, char* argv[]){
int fd = open("text.txt", O_RDONLY);
if (fd == -1){
printf("%s\n", strerror(errno));
return -1;
}
else {
int func = lseek(fd, 0, SEEK_END);
printf("%d bytes in size\n", func);
char* ptr = (char*)malloc(sizeof(char)*func + 1);
read(fd, ptr, func);
printf("%s", ptr);
free(ptr);
}
close(fd);
return 0;
}```

Answer 1

You need to move back to the beginning of the file before the read.
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int main(int argc, char* argv[]){
int fd = open("text.txt", O_RDONLY);
if (fd == -1){
printf("%s\n", strerror(errno));
return -1;
}
else {
int size = lseek(fd, 0, SEEK_END);
printf("%d bytes in size\n", size);
char* ptr = (char *) malloc(sizeof(char) * size + 1);
lseek(fd, 0, SEEK_SET); // move back to the beginning
read(fd, ptr, size);
printf("%.*s", size, ptr);
free(ptr);
}
close(fd);
return 0;
}
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int main(int argc, char* argv[]){
int fd = open("text.txt", O_RDONLY);
if (fd == -1){
printf("%s\n", strerror(errno));
return -1;
}
else {
int size = lseek(fd, 0, SEEK_END);
printf("%d bytes in size\n", size);
char* ptr = (char *) malloc(sizeof(char) * size + 1);
lseek(fd, 0, SEEK_SET); // move back to the beginning
read(fd, ptr, size);
printf("%.*s", size, ptr);
free(ptr);
}
close(fd);
return 0;
}
(venv) [ttucker#zim stackoverflow]$ cat text.txt
asdf
qwer
sdfg
(venv) [ttucker#zim stackoverflow]$ gcc -o print print.c
(venv) [ttucker#zim stackoverflow]$ ./print
15 bytes in size
asdf
qwer
sdfg