Problem in reading inputs

**Bargi** · 06-18-2008

Hi,

The following code is not working since fgets read the newline character when enter is pressed......

I have used fflush but this not working , can anybody let me know the correct way ?

Code:


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

struct student
{
    int roll_no;
    char name[25];
    char city[25];
    char course[10];
};

int main()
{ 
     int number, i;

     struct student s[22];

     printf("\n STUDENT RECORD PROGRAME");
     printf("\nEnter The No. Of Records to Enter");
     scanf("&#37;d",&number);
     printf("\nEnter The Data Of students");

     for(i= 1;i<=number; i++) {
     printf("\nEnter Name:"); 
     fflush(stdin);
     fgets(s[i].name, sizeof(s[i].name), stdin);
     
     printf("\nEnter Roll No.:");
     scanf("%d",&s[i].roll_no);

     printf("\nEnter City:");
     fgets(s[i].city, sizeof(s[i].city), stdin);

     printf("\nEnter Course:");
     fgets(s[i].course, sizeof(s[i].course), stdin);
     }

     printf( "\n The Details Of Student Are:\n");

     for(i= 1;i<=number; i++)  {

     printf("\n Enter Name: %s",s[i].name);
     printf("\nRoll No.:%d",s[i].roll_no);
     printf("\n  City:%s",s[i].city);
     printf("\n Course:%s",s[i].course);

     }

}

Thanks

**Elysia** · 06-18-2008

Flushing the input buffer is undefined, so it never works reliably.
You will need another way of flushing the input buffer. See link.
Or you can always use fgets and convert the data with strtol or similar.

**matsp** · 06-18-2008

Let me guess that you are using Linux, where fflush(stdin) is not "working".

You should not use fflush(stdin), because fflush(stdin) [or any other input file] is undefined by the ISO/ANSI C standard. It happens to work in certain compilers on certain OS's, but in other situations it may even crash your program. Instead, use a function to flush the input buffer after scanf(), e.g.

Code:

void clearinput(FILE *fin)
{
   int ch;
   while((ch = fgetc(fin)) != '\n' && ch != EOF) ;
}

--
Mats

**Bargi** · 06-18-2008

Thanks matsp,

It's working fine but now I have to press enter 2 times.... may be due to the

fgetc(fin)

in function .
Is there any way that I can directly check for newline without using fgetc() ??

Thanks

**Elysia** · 06-18-2008

No, there isn't.
You can avoid the issue altogether by using fgets all the time.

**matsp** · 06-18-2008

Originally Posted by Bargi

Thanks matsp,

It's working fine but now I have to press enter 2 times.... may be due to the in function .
Is there any way that I can directly check for newline without using fgetc() ??

Thanks

As Elysia says, there's no way to check if there's anything in the input buffer or not.

Perhaps that's because your fflush() in the original code is in the wrong place, which I presume is where you put your clearinput() call?

--
Mats

**C_ntua** · 06-18-2008

Don't know if this is correct (probably not?) or what you want:

Code:

FILE * chk_eol (FILE *fin, int *found)
{
   char c;
   FILE *save_fin = fin;
   
   c = fgetc(fin);
   if (c == '\n')
      *found = 1;
   else
      *found = 0;
   
   return save_fin;
}

so you ll use fgetc() but you ll have the previous value of the pointer restored, so no harm done I suppose.
and you call by
fin = chk_eol(fin, &found);
and found says if the next character is '\n' or not

**Elysia** · 06-18-2008

chk_eol is non-standard.

**matsp** · 06-18-2008

Originally Posted by C_ntua

Don't know if this is correct (probably not?) or what you want:

Code:

FILE * chk_eol (FILE *fin, int *found)
{
   char c;
   FILE *save_fin = fin;
   
   c = fgetc(fin);
   if (c == '\n')
      *found = 1;
   else
      *found = 0;
   
   return save_fin;
}

so you ll use fgetc() but you ll have the previous value of the pointer restored, so no harm done I suppose.
and you call by
fin = chk_eol(fin, &found);
and found says if the next character is '\n' or not

Copying the file-pointer won't retain where in the input buffer the current input is, which I presume is the purpose you are using "save_fin" for.

It also won't work, as fgetc() will read from the input (and block until you press enter) if there isn't anything in the input buffer.

So, it won't actually do what you want. If you KNOW that there is more input available in the input buffer, you could "peek" at it by calling fgetc() and then fungetc() - but that still fails in the same way as the code I posted if you don't have any pending data in the input buffer.

--
Mats

**C_ntua** · 06-18-2008

Originally Posted by Elysia

chk_eol is non-standard.

what do you mean?

**Elysia** · 06-18-2008

Originally Posted by C_ntua

what do you mean?

It means some compilers may have it, and some not. In other words, it's not part of the standard, it's a compiler extension, because I just checked MSDN, and there's no such function.

**matsp** · 06-18-2008

Originally Posted by Elysia

It means some compilers may have it, and some not. In other words, it's not part of the standard, it's a compiler extension, because I just checked MSDN, and there's no such function.

c_ntua posted code that implements chk_eol, not suggesting that it's a standard function at all. However, it is my opinion that the posted code doesn't at all work.

--
Mats

**Elysia** · 06-18-2008

I'm slow >_<
But reading with fgetc is bad. If there is nothing in the input buffer, it will wait for input.

**C_ntua** · 06-18-2008

Originally Posted by Elysia

It means some compilers may have it, and some not. In other words, it's not part of the standard, it's a compiler extension, because I just checked MSDN, and there's no such function.

Well, it is my function if that is what you mean. Just made it up. That's why I said I don't know if it is correct.

**Elysia** · 06-18-2008

Originally Posted by C_ntua

Well, it is my function if that is what you mean. Just made it up. That's why I said I don't know if it is correct.

I missed that >_<

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