Standard I/O

A process can take advantage of the entire C library for dealing with I/O. In addition to the I/O interface provided by the C library, a process may also use POSIX I/O services such as open(), read(), or write(), as well as POSIX socket services such as socket(), bind(), and connect().

The following program can be run as a process and illustrates the way in which the C library can be used from a process.

Example 3-2 Using the C Library from a Process

#include <stdio.h>
#include <stdlib.h>
#include <chorus.h>
#define  BUF_SIZE 80
struct stat st;
int main(int argc, char** argv, char** envp)
{
   FILE* file;
   FILE* filew;
   char* buf;
   int res;
   if (argc != 2 && argc != 3) {
      fprintf(stderr, "Usage: %s filename\n", argv[0]);
      exit(1);
   }
   file = fopen(argv[1], "r");
   if (file == NULL) {
      fprintf(stderr, "Cannot open file %s\n", argv[1]);
      exit(1);
   }
   res = stat(argv[1], &st);
   if (res < 0) {
      fprintf(stderr, "Cannot stat file\n");
      exit(1);
   }
   printf("File size is %d mode 0x%x\n", st.st_size, st.st_mode);
   buf = (char*) malloc(BUF_SIZE);
   if (buf == NULL) {
      fprintf(stderr, "Cannot allocate buffer\n");
      exit(1);
   }
   bzero(buf, BUF_SIZE);
   res = read(fileno(file), buf, 80);
   if (res == -1) {
      fprintf(stderr, "Cannot read file\n");
      exit(1);
   }
   printf("%s\n", buf);
   if (argv[2] != NULL) {
      filew = fopen(argv[2], "w");
      if (filew == NULL) {
         fprintf(stderr, "Cannot open file %s\n", argv[2]);
         exit(1);
      }
      printf("Type any input you like: \n");
      do {
         scanf("%80s", buf);
         printf("buf=%s\n", buf);
         fprintf(filew, "%s", buf);
         printf("buf=%s\n", buf);
      } while (buf[0] != 'Q');
   }
   exit(0);
}

Referencing argv[0] without checking if argc is greater than zero can cause the process to incur an exception and be deleted.