gets() causing output error

Question

error in output due to gets()...as it can be seen in the image ... program prints 0 before waiting for user to enter the string. I need to read a string of "click X" format where X is a integer. Is there any alternative to gets() to use in this situation?

 #include<stdio.h>
#include<stdlib.h>
int main()
{
    int n,k,i;
    char action[10];
    int *open;
    scanf("%d%d",&n,&k);                                    
    open= calloc( sizeof(int),n);               

    for(i=0;i<n;i++)
    {
        open[i]=0;
    }


    for(i=0;i<k;i++)
    {                                                     
        //gets to read an input  as "click 1"
      gets(action); 
      printf("%d\t%c",i,action[6]);     
    }
    free(open);                                                         
    return 0;
}

Elaborate what? Did you read all the answers to the linked question? — interjay, Sep 29 '15 at 11:16
i got your point. is there any alternative for this situation? — smasher, Sep 29 '15 at 11:21
Yes, the alternative is to do one of the things suggested in the answers to the duplicate question. — interjay, Sep 29 '15 at 11:22
I am not sure if this is duplicate possible cause is calloc of int whereas gets is for char ( I may be completely wrong though ) — asio_guy, Sep 29 '15 at 11:43

Basile Starynkevitch · Answer 1 · 2015-09-29T11:30:59.517

1

Your action is probably declared too short. Try

  char action[64];

instead.

Then replace

  gets(action); /// BAD CODE

with

  fflush (NULL);
  memset (action, 0, sizeof(action));
  fgets  (action, sizeof(action), stdin);

You should never use gets, it is obsolete.

^{(use fflush to flush output buffer; the memset is clearing the action buffer; the fgets is reading at most 63 bytes in it from stdin, so you are sure action is ending will a null byte as every C string should)}

You should ask your compiler to give you all warnings and debug info, e.g. use gcc -std=c99 -Wall -Wextra -g if using GCC.

You should learn to use the debugger (e.g. gdb)

edited Sep 29 '15 at 11:30

answered Sep 29 '15 at 11:19

Basile Starynkevitch

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The issue here is the `gets` call not asking for user input at all. Switching to `fgets` will not change that. Reading the duplicate question will. – interjay Sep 29 '15 at 11:22
why have you deducted 1 from sizeof(action) – smasher Sep 29 '15 at 11:29
@smasher: my mistake, corrected! – Basile Starynkevitch Sep 29 '15 at 11:31

ashiquzzaman33 · Answer 2 · 2015-09-29T12:19:28.620

0

After 'scanf' use

getchar();

to consume extra newline. As 'scanf' can not discard newline, first iteration of 'gets' take the newline.

Don't use 'gets', use 'fgets' instead

You can use 'fgets()' as

fgets(action, sizeof(action), stdin);

edited Sep 29 '15 at 12:19

answered Sep 29 '15 at 11:15

ashiquzzaman33

5,781
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True, but does not answer the question. – interjay Sep 29 '15 at 11:16
how to use fgets() in this situation as i am not using any file stream? – smasher Sep 29 '15 at 11:17
yup, it solved the problem probably consuming extra newline – smasher Sep 29 '15 at 11:28
@interjay, answer edited. – ashiquzzaman33 Sep 29 '15 at 13:12

gets() causing output error

2 Answers2