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 NETBSD

pcap_open_offline

PCAP_OPEN_OFFLINE(3)					     Library Functions Manual					      PCAP_OPEN_OFFLINE(3)

NAME

       pcap_open_offline, pcap_fopen_offline - open a saved capture file for reading

SYNOPSIS

       #include <pcap/pcap.h>

       char errbuf[PCAP_ERRBUF_SIZE];

       pcap_t *pcap_open_offline(const char *fname, char *errbuf);
       pcap_t *pcap_fopen_offline(FILE *fp, char *errbuf);

DESCRIPTION

       pcap_open_offline() is called to open a ``savefile'' for reading.

       fname  specifies  the  name of the file to open. The file can have the pcap file format as described in pcap-savefile(5), which is the file
       format used by, among other programs, tcpdump(8) and tcpslice(1), or can have the pcap-ng file format, although not all pcap-ng	files  can
       be read.  The name "-" in a synonym for stdin.

       Alternatively,  you  may  call pcap_fopen_offline() to read dumped data from an existing open stream fp.  Note that on Windows, that stream
       should be opened in binary mode.

RETURN VALUE

       pcap_open_offline() and pcap_fopen_offline() return a pcap_t * on success and NULL on failure.  If NULL is returned, errbuf  is	filled	in
       with an appropriate error message.  errbuf is assumed to be able to hold at least PCAP_ERRBUF_SIZE chars.

SEE ALSO

       pcap(3), pcap-savefile(5)

								   5 April 2008 					      PCAP_OPEN_OFFLINE(3)