reading with pread() and writing with pwrite() in c - c

Question

My program(below) writes(with pwrite()) text to a file and reads(with pread()) from the file. My problems are pread function doesn't read my text from file and what's wrong with close function(last part of program)? Results is in the second part. Where is my mistake?
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
int main()
{
int fd, nr, nr2, nw, nw2;
char fl_nm[]={"file_io/pwrite.txt"};
char buf_wr[]={"hello everyone this is first text\n"};
char buf_wr2[]={"Did you miss me? Don't afraid\n"};
char buf_rd[120];
char buf_rd2[120];
//open file
fd = open(fl_nm, O_RDWR|O_CREAT, 0777);
nw = pwrite(fd, &buf_wr, strlen(buf_wr), 14);
//error checking
if(fd == -1){
perror("[error in open]\n");
}
else if(nw == -1){
perror("[error in write]\n");
}
else{
/*if open and write process are okey, read first write data
* from file*/
nr = read(fd, &buf_rd, sizeof(buf_rd));
//display succeeded message about first write and open process
printf("[file is opened]\n");
printf("[succeeded write(1) process]\n");
//read process error control
if(nr == -1){
perror("[error in read]\n");
} else{
printf("[reading(1) data] from %s\n", fl_nm);
printf("[%s]\n", buf_rd);
}
}
//second write process.
nw2= pwrite(fd, &buf_wr2, strlen(buf_wr2), 30);
//write error checking
if(nw2 == -1){
perror("[error in write 2]\n");
}else{
/*if write process is correct
* second read process*/
nr2 = read(fd, &buf_rd2, sizeof(buf_rd));
printf("-----------------------------------\n");
printf("[succeeded write(2) process]\n");
printf("[reading(2) data] from %s\n", fl_nm);
printf("[%s]\n", buf_rd2);
}
//close file
close(fd);
//error checking for close process
if(close(fd) == -1){
perror("[error in close]\n");
}else{
printf("[succeeded in close]\n");
}
return 0;
}
Result:
$ gcc pwrite.c -o pwrite
$ ./pwrite
[file is opened]
[succeeded write(1) process]
[reading(1) data] from file_io/pwrite.txt
[]
-----------------------------------
[succeeded write(2) process]
[reading(2) data] from file_io/pwrite.txt
[]
[error in close]
: Bad file descriptor

Answer 1

1) close() fails because you are closing the file twice:
//close file
close(fd);
//error check close process
if(close(fd) == -1){
After the first call to close(fd);, fd becomes indeterminate and the second call to close(fd) fails. You just need to remove the first call to close(fd);.
2) You are printing buf_rd as if it's a C-string. read() doesn't terminate buf_rd with a null byte.
3) You are writing at random offsets (14 and 30) using pwrite(). But read() reads from current offset - which means the starting byte could a null byte and thus %s stops printing right away (i.e. prints nothing). You are reading a lot more than what you write. That means read() is going to return less than the requested number of bytes. So use the return value of read() to get the number of bytes successfully read.
Instead, print each byte using a loop:
for (size_t l = 0; l < nr; l++)
printf("%c", buf_rd[l]);
and
for (size_t l = 0; l < nr2; l++)
printf("%c", buf_rd2[l]);

Answer 2

You're using pointers incorrectly, accessing to address of arrays should be with their names alone, not &name.
replace &buf_wr with buf_wr, accessing to incorrect address with &buf_wr to writing there will corrupt your stack and also variables defined inside stack
Edit:
replace
nw = pwrite(fd, &buf_wr, strlen(buf_wr), 14);
to
nw = pwrite(fd, buf_wr, strlen(buf_wr), 14);
and all other instances..