RE: [Dev-C++] scanf with gets

[Ioannis V. <iv...@at...>]

> -----Original Message-----
> From: dev...@li... 
> [mailto:dev...@li...] On Behalf 
> Of Andrι Macαrio Barros
> Sent: Friday, April 11, 2003 8:34 AM
> To: Dev-Cpp-Users
> Subject: [Dev-C++] scanf with gets
> 
> 
> Dear programmers,
> 
> I´m having to use the fflush command in the following code:
> 
> #include <stdio.h>
> #include <stdlib.h>
> 
> int main()
> {
>    char name[10];
>    int a, b, c;
> 
>    printf("Enter a-->");
>    scanf("%d", &a);
>    printf("Enter some name-->");
>    fflush(stdin);

The  behaviour of the above is undefined (e.g. the airplane may crash).
fflush() is intended to be used on output streams.

You can simply do:

getchar();



>    gets(name);


Extremelly Dangerous for buffer overflow (that is you must trust the user
very well, and he user must know the internals of your code). A better one:

fgets(name,10,stdin);





>    printf("Enter com b-->");
>    scanf("%d", &b);
>    printf("The sum of %d with %d is %d\n", a, b, a+b);
>    printf("And the name typed was %s\n", name);
>    system("PAUSE");
>    return 0;
> }
> 
> The reason is that if I don´t put it, the program doesn´t 
> wait for the name
> to be typed via keyboard. It passes directly to the other operator, b,
> indicating that the input buffer is loaded with something. I made some
> experiments with short int (hd), but nothing solved.
> 
> 1-Can anyone explain what is happening?



scanf() leaves the '\n' on the stream. Then gets() was reading and
interpreting it as if you entered an empty string.



> 2-What is the solution for don´t use the fflush?


getchar(); or something. You can even do a function in the style:


void clean_stdin()
{
  while(getchar()!='\n')
       ;
}



And use it. If you are going to use it with stream redirection in the style


myprogram <whatever.txt


for example,

you have to get EOF into account.





Ioannis Vranos
 
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