gets() does not read user input

Question

I am new to linked list, now I have little problems in population of nodes.

Here I could populate first node of linked list but the gets() function doesn't seems to pause the execution to fill the next node.

Output is like:

Var name : var
Do you want to continue ?y
Var name : Do you want to continue ?  // Here I cannot input second data

Here is my code:

struct data
{
    char name[50];
    struct data* next;
};
struct data* head=NULL;
struct data* current=NULL;
void CreateConfig()
{
    head = malloc(sizeof(struct data));
    head->next=NULL;
    current = head;
    char ch;
    while(1)
    {
        printf("Var name : ");
        gets(current->name);    //Here is the problem,
        printf("Do you want to continue ?");
        ch=getchar();
        if(ch=='n')
        {
            current->next=NULL;
            break;
        }
        current->next= malloc(sizeof(struct data));
        current=current->next;
    }
}

maybe you need to do type cast, add `(data *)` before every `malloc`, like this `(data *) malloc(sizeof(struct data))` — behzad.nouri, Nov 21 '11 at 18:38
@runnerup: That is a bad idea: http://stackoverflow.com/questions/1565496/specifically-whats-dangerous-about-casting-the-result-of-malloc — ChrisWue, Nov 21 '11 at 18:42
What is the problem you are seeing exactly? Does the program crash or something else? — ChrisWue, Nov 21 '11 at 18:45
function "malloc" returns a void pointer, you should manually convert it to (data*) type — zebrilo, Nov 21 '11 at 18:45

score 7 · Accepted Answer · edited May 23 '17 at 10:34

This happens because:

ch=getchar();

read either y or n from the input and assigns to ch but there a newline in the input buffer which gets read by the gets in the next iteration.

To fix that you need to consume the newline following the y/n the user enters. To do that you can add another call to getchar() as:

ch=getchar(); // read user input
getchar();    // consume newline

Also the function fgets should be used in place of gets. Why?

Cacho Santa · Answer 2 · 2011-11-21T19:00:11.590

It's exactly what @codaddict said. You need to clean the buffer.

void fflushstdin( void )
{
    int c;
    while( (c = fgetc( stdin )) != EOF && c != '\n' );
}

You can read this links that explains it very well:

c-faq
And this mdsn if you are on windows.

One more thing, try to always use fgets -instead of gets-, as it is impossible to prevent buffer overflows if you are using gets.

You could read the section "Use of safe libraries" at this link

score 0 · Answer 3 · answered Nov 21 '11 at 18:54

0

you should also add a line like

 current->next = 0;

after

 current=current->next;

to ensure that the last element's next is not dangling.

answered Nov 21 '11 at 18:54

Walter

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gets() does not read user input

3 Answers3