Question

I have a problem when using a user input method which allow validates the input.
I require to return the input after its been validated.

char* getvalidinputnumber(int length, char prompt[],int base)
    {
        char* user_input = calloc(length+1,sizeof(char));

        fflush(stdin);
        fflush(FILE *);

        /*Prompts & Gets the users input and saves it in user_input*/
        do {
            printf("\n %s", prompt); 
            fgets(user_input,length+1,stdin); 
            /*printf("\n##Entered %s : ", user_input);*/
        } while(!isnumeric(user_input,base) && strlen(user_input) != length);

        fflush(stdin); 
        return(user_input);
    }

When calling this function within my main like….

while (strcmp(user_input,"00000000") != 0)
{
    user_input = getvalidinputnumber(8, "Enter HEX Value",16);
}

It also does the following …

Enter HEX Value

Enter HEX Value

Twice rather than just once and when i enter a hex value it returns the hex correct but then runs twice again ive tryed using fflush but this doesnt seem to solve it.

How could i solve this or is there a better way to get the input for example using scanf?

Answer 1

fflush(stdin)

Causes an Undefined Behavior! fflush() should only be used on streams open for output, not input.