Using C language to use system calls Post: 302734115

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Homework and Emergencies Homework & Coursework Questions Using C language to use system calls Post 302734115 by Corona688 on Wednesday 21st of November 2012 03:53:45 PM

11-21-2012

Registered User

It's possible to do it either way. Line-by-line is probably easier.

Your using scanf incorrectly every time you use it. You can't store a string in a char, since a string is a char array, and you shouldn't be using scanf to read raw data. Read lines then feed them into sscanf, or your code may get stuck in infinite loops whenever the user types something wrong.

I'd do this:

Code:

while(1)
{
        char buf[512];
        int selection;
        if(fgets(buf, 512, stdin) == NULL) break; // Read line, quit on error
        // Convert line into number
        if(sscanf(buf, "%d", &selection) != 1)
        {
                fprintf(stderr, "you did not type a number\n");
                continue;
        }

        switch(selection)
        {
...
        }
}

Also, you cannot store an entire string inside a single character. You'll need to feed sscanf an array for the filenames. Something like this:

Code:

char fname[512];
printf("Please enter a filename:\n");
// Read a line
fgets(fname, 512, stdin);
// chop the newline off the end of the line
for(n=0; fname[n]; n++) if(fname[n] == '\n') fname[n]='\0';

System calls you'll need are unlink to remove files, open to read or create files, read to read from files, write to write to files, and close to close file descriptors once you're done.

Include files you'll need for all those are

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

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LEARN ABOUT MINIX

gets

GETS(3) 						     Library Functions Manual							   GETS(3)

NAME

       gets, fgets - get a string from a stream

SYNOPSIS

       #include <stdio.h>

       char *gets(char *s)
       char *fgets(char *s, int n, FILE *stream)

DESCRIPTION

       Gets  reads  a string into s from the standard input stream stdin.  The string is terminated by a newline character, which is replaced in s
       by a null character.  Gets returns its argument.

       Fgets reads n-1 characters, or up through a newline character, whichever comes first, from the stream into the string s.  The last  charac-
       ter read into s is followed by a null character.  Fgets returns its first argument.

SEE ALSO

       puts(3), getc(3), scanf(3), fread(3), ferror(3).

DIAGNOSTICS

       Gets and fgets return the constant pointer NULL upon end of file or error.

BUGS

       Gets deletes a newline, fgets keeps it, all in the name of backward compatibility.

       Gets is not present in the Minix-vmd C library for reasons that should be obvious.  Use fgets instead.

7th Edition							   May 15, 1985 							   GETS(3)