Write a small C program newcat which performs exactly as old

Write a small C program newcat, which performs exactly as oldcat (shown below), but uses UNIX system calls for input/output. Specifically, use the UNIX system calls whose prototypes are shown below:

int read(int fd, char *buf, int n); ........... int write(int fd, char *buf, int n);

int open(char *name, int accessmode, int permission); ........... int close(int fd);

To open a file for read, you can use the symbolic constant O_RDONLY   defined   in   fcntl.h header file to specify the accessmode. Simply pass 0 for permission. That is, the code will appear as follows:

fd = open (filename, O_RDONLY, 0);

You will need the following header files: sys/types.h, unistd.h and fcntl.h

Compile and test the program. Produce a script file containing the source code and several executions. Please be sure to include test situations where a file to be concatenated could not be opened, and where no command line argument is provided. Thanks a lot for your help!!!

#include <stdio.h>

#include <stdlib.h>

/* oldcat: Concatenate files */

int main(int argc, char *argv[])

{

   void filecopy(FILE *, FILE *); /* prototype for function */

   FILE *fp;

   char *prog = argv[0]; /* program name for errors */

   if (argc == 1) /* no args; copy standard input */

      filecopy(stdin, stdout);

   else

      while (--argc > 0)

         if ((fp = fopen(*++argv, \"r\")) == NULL) {

            fprintf(stderr, \"%s: can\'t open %s\ \", prog, *argv);

            exit(-1);

         } else {

            filecopy(fp, stdout);

            fclose(fp);

         }

   exit(0);

}

/* filecopy: copy file ifp to ofp */

void filecopy(FILE *ifp, FILE *ofp)

{

   int c;

   while ((c = getc(ifp)) != EOF)

      putc(c, ofp);

}

Solution

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
/* oldcat: Concatenate files */

int main(int argc, char *argv[])

{

   void filecopy(int, int); /* prototype for function */

   int fd; //FILE *fp;

   char *prog = argv[0]; /* program name for errors */

   if (argc == 1) /* no args; copy standard input */

      filecopy(stdin, stdout);

   else

      while (--argc > 0)

       if((fd=open(*++argv, O_RDONLY))== -1){// if ((fp = fopen(*++argv, \"r\")) == NULL) {

            fprintf(stderr, \"%s: can\'t open %s\ \", prog, *argv);

            exit(-1);

         } else {

            filecopy(fd, stdout);

            close(fd);//fclose(fp);

         }

   exit(0);
}

/* filecopy: copy file ifp to ofp */

//void filecopy(FILE *ifp, FILE *ofp)
void filecopy(int ifp, int ofp)
{

   int c;
   char a[256];
   read(ifp, a, 256);//while ((c = getc(ifp)) != EOF)

   write(ofp, a, strlen(a)); //putc(c, ofp);

}