Question

Modify the bellow program by using only system calls to perform the task. These

system calls are open,read,write, and exit .Use text and binary files to test your programs.

#include <stdio.h>

void main(int argc,char **argv)

{

FILE *fp1, *fp2;

char ch, buf[20], *pos;

int n;

pos = buf;

if ((fp1 = fopen(argv[1],"r")) == NULL)

{

puts("File cannot be opened");

exit(1);

}

fp2 = fopen(argv[2], "w");

while ((n = fread(pos, sizeof(char), 20, fp1)) == 20)

{

fwrite(pos, sizeof(char), 20, fp2);

}

fwrite(pos, sizeof(char), n, fp2);

fclose(fp1);

fclose(fp2);

exit(0);

}

Answer 1

Following is the program

#include <stdio.h>
#include<fcntl.h>
#include<errno.h>

void main(int argc,char **argv)

{

//FILE *fp1, *fp2; no longer needed

char ch, buf[20], *pos;

int n;

pos = buf;

//created file descripter for files
int fp1, fp2;

//fp1 = fopen(argv[1],"r") changed to
if ((fp1 = open(argv[1], O_RDONLY)) == -1)

{

puts("File cannot be opened");

exit(1);

}

//fp2 = fopen(argv[2], "w"); changed to
fp2 = open(argv[2], O_WRONLY);

//n = fread(pos, sizeof(char), 20, fp1) changed to
while ((n = read (fp1, pos, 20)) == 20)

{

//fwrite(pos, sizeof(char), 20, fp2); changed to
write (fp2, pos, 20);

}

//fwrite(pos, sizeof(char), n, fp2);changed to
write (fp2, pos, n);

//fclose(fp1); changed to
close(fp1);

//fclose(fp2); changed to
close(fp2);

exit(0);

}

------------------------------------------

In Short, new syntax is this and it is no longer required to enter Size of Byte parameter,

int open (const char* Path, int flags [, int mode ]);

int close(int fd); 

size_t read (int fd, void* buf, size_t cnt);  

size_t write (int fd, void* buf, size_t cnt); 

as for detailed study of system calls regarding open write read and close you can use this reference:

https://www.geeksforgeeks.org/input-output-system-calls-c-create-open-close-read-write/