Thread: I'm missing something obvious

I'm trying to complete an excercise to learn unix system calls and one of the functions in the program was giving me only partial output. So I wrote a test program that is almost identical to the one linked with the rest of the program that works fine. I've gone over this for a solid day. Anyway, here's the code to what works:

Code:

#include "hotel.h"
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

#define LNAME 22
#define FNAME 19

char buf[NLINES];

void gname(int, int *);

int
main()
{
    int index = 0;

    printf("Enter last name: ");
    gname(LNAME, &index);
    printf("Enter first  name: ");
    gname(FNAME, &index);
    printf("%s", buf);
}

gname(int i, int *index)
{
    int j, count = *index;
    char c;


    if (i == LNAME)
        j = i - 2;
    else if (i == FNAME)
        j = (LNAME + FNAME) - 1;

    while ( (c = getchar()) != '\n' && c != EOF && count < j) {
        buf[count] = c;
        count++;
    }

    if (i == LNAME) {
        buf[count] = ',';
        buf[++count] = ' ';
        *index = ++count;
    }

    if (i == FNAME) {
        for (count; count < j; ++count)
            buf[count] = ' ';
        buf[count] = '\n';
    }
}

gname(int i, int *index)
{
    int j, count = *index;
    char c;


    if (i == LNAME)
        j = i - 2;
    else if (i == FNAME)
        j = (LNAME + FNAME) - 1;

    while ( (c = getchar()) != '\n' && c != EOF && count < j) {
        buf[count] = c;
        count++;
    }

    if (i == LNAME) {
        buf[count] = ',';
        buf[++count] = ' ';
        *index = ++count;
    }

    if (i == FNAME) {
        for (count; count < j; ++count)
            buf[count] = ' ';
        buf[count] = '\n';
    }
}

This works just fine.
it will output and print the following
Enter last name: ted
Enter first name: danson
danson, ted

The hotel.h file just contains two extern variables:
extern int fd; /*a file descriptor for global use*/
#define NLINES 41
#define MAXROWS 10
extern char buf[NLINES];

Then I copy this file to the directory with the rest of the files, make a few modifacations and don't get what I expect.

Code:

#include "hotel.h"
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <stdbool.h>

#define LNAME 22
#define FNAME 19

char buf[NLINES];
int fd;

void gname(int, int *);

bool
addguest(int *roomnum)
{
    int room, index = 0;
    off_t offset;

    if (!findfree(&room))
        return false;
    else
        *roomnum = room;

    offset = (room - 1) * NLINES;
    if (lseek(fd, offset, SEEK_SET) < 0) {
  perror("problem with lseek in addguest");
        exit(-1);
    } 

    printf("Enter last name: ");
    gname(LNAME, &index);
    clearstdin();
    printf("Enter first  name: ");
    gname(FNAME, &index);
    printf("%s", buf);
}

void
gname(int i, int *index)
{
    int j, count = *index;
    char c;


    if (i == LNAME)
        j = i - 2;
    else if (i == FNAME)
        j = (LNAME + FNAME) - 1;

    while ( (c = getchar()) != '\n' && c != EOF && count < j) {
        buf[count] = c;
        count++;
    }

    if (i == LNAME) {
        buf[count] = ',';
        buf[++count] = ' ';
        *index = ++count;
    }

    if (i == FNAME) {
        for (count; count < j; ++count)
            buf[count] = ' ';
        buf[count] = '\n';
    }
}

this will prompt the same, with the use of the clearstdin function, otherwise it will output
Enter last name: Enter first name:
the clearstdin function is:

Code:

void
clearstdin()
{
    char c;
    while ((c = getchar()) != NULL && c != '\n' && c != EOF)
}

so with this function I get the proper prompts but the output is:
, ted
Maybe it's the clearstdin function that's causing the problem but if it is I don't see how.
Thanks in advance.

Since getchar() returns an int, you may want to have int c; instead in clearstdin()

I don't suppose it occurred to you to try it without calling clearstdin();

Well lets see, the original worked fine without it.

With it, you're missing half your input (the whole of the 2nd line)

If you really want proof, try printing out each character that clearstdin() gets rid of, and see if it contains "danson".

Originally Posted by crash88

too bad it wasn't stdin. the output was this when I tried writing each character to the screen
crash@venus::~/programs/usp/ch2$ ./frontdesk file.txt


1 getoccupier
2 freeroom
3 addguest
4 findfree

choice: 3
Enter last name: danson
10097110115111110Enter first name: ted
Guest was added to room 1.
Return to continue:


1 getoccupier
2 freeroom
3 addguest
4 findfree

choice: 1
What room: 1
, ted
is in room 1.
Return to continue:

even looking in file.txt it is the same as what's outputted to the screen.

What the ........ is that? Oh, I know what it is, it's just what Salem said it was:
100 = d
97 = a
110 = n
115 = s
111 = o
110 = n

You should probably actually learn to debug instead of just crying about everything "not working" and everyone being wrong when they're not.


Quzah.