NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/9987

Text File | 1996-08-05 | 4.5 KB | 190 lines

Path: mail2news.demon.co.uk!genesis.demon.co.uk
From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: HELP!
Date: Thu, 14 Mar 96 20:02:17 GMT
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Message-ID: <[e-mail]>
References: <4htsjm$[e-mail]> <[e-mail]>
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In article <[e-mail]>
           [e-mail] "Steve Fogoros" writes:

>Teddy Bear wrote:
>>
>> Can anyone please help me my giving me a sample programme?
>> I need to write a program that will enter and record an individual's
>> details
>> search (by name) and display an individual's details
>> Delete an individual's details
>> Save and restore the entire list to/from a disk file
>>
>> Emergency!
>> Thanks
>> my e-mail add is at [e-mail]
>
>Here is a most basic sample program:
>
>#include "stdio.h"
>#include "stdlib.h"
>#include "string.h"

These should be:

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

>void enter(void);
>void show(void);
>void delete(void);
>
>FILE *fi, *fo;
>
>void main(void)

main returns int in C.

 int main(void)

>{
>   printf("1. enter a record\n");
>   printf("2. show a record\n");
>   printf("3. delete a record\n");
>   printf("4. exit\n");
>   printf("Press 1, 2, 3, or 4 then enter\n");
>
>   switch((char)getc(stdin))

getc(stdin) is more commonly called getchar()

The (char) cast has no effect other than possibly to introduce implementation
defined behaviour - you're better off without it. It is worth noting as
a distantly related issue that character constants such as '1' have type int
in C.

>   {
>   case '1': getc(stdin); enter(); break;
>   case '2': getc(stdin); show(); break;
>   case '3': getc(stdin); delete(); break;
>   case '4': exit(0); break;
>   default: printf("bad selection. program terminated\n"); exit(0); break;
>   }

    return 0;

>}
>
>void enter(void)
>{
>   char buff[80];
>
>   printf("Enter data followed by return key\n");
>   fgets(buff,79,stdin);

This is OK but you could also have written:

    fgets(buff,80,stdin);

or better still

    fgets(buff,sizeof buff,stdin);

the 2nd argument specifies the maximum number of characters that fgets()
will write to the buffer including the terminating '\0'

>
>   fi = fopen("dfile","a");
>   if(fi == 0)

Tha's fine but you might consider demonstrating the pointer comparison
explicitly with:

    if(fi == NULL)

>   {
>      printf("unable to open dfile. program terminated\n");
>      exit(0);

Since this is a failure state you might also consider:

       exit(EXIT_FAILURE);

EXIT_SUCCESS and EXIT_FAILURE are defined in stdlib.h. 0 return is an
alternative to EXIT_SUCCESS for indicating success.

>   }
>
>   fprintf(fi,"%s",buff);
>
>   fclose(fi);
>}
>
>void show(void)
>{
>   char srch[80], buff[80];
>
>   printf("Enter search string and enter\n");
>   fgets(srch,79,stdin);

Same as before.

>   srch[strlen(srch)-1] = 0;

This is dangerous - it is possible for fgets() to put a 0 length string in
srch. It is also possible that the last character before '\0' is not '\n',
not to mention the possibility of fgets() writing no characters to srch
because of an end-of-file or error condition. Some of these thing can perhaps
be ignored for keyboard input (but IMHO it is not a good idea) there
is a simple trick that has recently been making the rounds of comp.lang.c
which copes with the first two problems:

     strtok(srch, "\n");

>   printf("\n");

There is also putchar('\n') which is the tool designed for this particular
job. I know others prefer the uniformity of using printf everywhere.

>   fi = fopen("dfile","r");
>   if(fi == 0)
>   {
>      printf("unable to open dfile. program terminated\n");
>      exit(0);
>   }
>
>   while(!feof(fi))
>   {
>      fgets(buff,79,fi);
>      if(feof(fi)) break;
>      if(strstr(buff,srch)) printf("%s",buff);
>   }

It is quite rare that you need to use feof() needs to be used.
Most standard library function have return values and they are there to
be used. So:

    while(fgets(buff,sizeof buff,fi) != NULL)
    {
        if(strstr(buff,srch)) printf("%s",buff);
    }

The loop test exits the loop on both an end-of-file and error condition
If you wanted to find out wich occurred you could use ferror() or feof()
here.

>   fclose(fi);
>}

...

--
-----------------------------------------
Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
-----------------------------------------