gets() not working for me [duplicate]

This question already has answers here: scanf() leaves the newline character in the buffer (7 answers) Closed 5 years ago.

Quick issue with my code. Please look in the function enter(). When I request the name, and use gets(), it just skips it as if nothing was there, and jumps to requesting the age. What am I doing incorrectly?

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

#define RECORDS 30
#define LEN 20

/*Questions
Formatting display() - can we use spaces to format?
Is the patient structure supposed to be global or local in enter()?
Why doesn't printf("name: "); scanf("%s", name); require &name?
Make sure you account for first and last names, use getline or something
*/

void enter();

struct patient
{
    char name[LEN];
    int age;
    double highBP, lowBP, riskFactor;
};

struct patient * db[RECORDS];
int counter = 0;

main()
{
    int flag = 1;

    while (flag == 1)
    {       
        printf("---------------------------------------------------------\n");
        printf("|\t(N)ew record\t(D)isplay db\t(U)pdate record |\n");
        printf("|\t(L)oad disk\t(W)rite disk\t(E)mpty disk    |\n");
        printf("|\t(S)ort db\t(C)lear db\t(Q)uit          |\n");
        printf("--------------------------开发者_开发知识库-------------------------------\n");
        printf("choose one: ");

        char selection, selectionstr[3];
        scanf("%s",selectionstr);
        selection = selectionstr[0];        

        //printf("selection %c\n", selection);

        if ((selection == 'n') || (selection == 'N'))
        {
            //New record
            enter();
        }

            // Options omitted...

        else
        {
            printf("not a vaild input\n");  
        }
    }
}

void enter()
{
    if (counter < 30)
    {
        FILE *fptr;
        fptr = fopen("db.txt", "a");

        char name[LEN];
        int age;
        double highBP, lowBP;
        printf("name: "); //scanf("%s", name);
        gets(name);
        printf("age: "); scanf("%d", &age);
        printf("high bp: "); scanf("%lf", &highBP);
        printf("low bp: "); scanf("%lf", &lowBP);
        struct patient temp;
        strcpy(temp.name, name);
        temp.age = age;
        temp.highBP = highBP;
        temp.lowBP = lowBP;

        if ((highBP < 120) && (lowBP < 80))
            temp.riskFactor = 0;

        if (((highBP <= 120) && ((lowBP > 80) && (lowBP <= 90))) || ((highBP <= 80) && ((lowBP > 120) && (lowBP <= 130))))
            temp.riskFactor = 1;

        if (((highBP <= 120) && ((lowBP > 90) && (lowBP <= 100))) || ((highBP <= 80) && ((lowBP > 130) && (lowBP <= 140))))
            temp.riskFactor = 4;

        else
            temp.riskFactor = 5;

        if ((temp.riskFactor > 0) && (temp.age > 50))
            temp.riskFactor += 0.5;

        db[counter] = &temp;
        //fprintf(fptr, "%s, %d, %f, %f, %f\n", db[counter]->name, db[counter]->age, db[counter]->highBP, db[counter]->lowBP, db[counter]->riskFactor);
        printf("%s, %d, %f, %f, %f\n", db[counter]->name, db[counter]->age, db[counter]->highBP, db[counter]->lowBP, db[counter]->riskFactor);
        counter++;

        fclose(fptr);
    }

    else
        printf("database full");


    /*db[counter] = (struct patient *) malloc(sizeof(struct patient));


    printf("name: "); scanf("%s", (*db[counter]).name);
    printf("age: "); scanf("%d", (*db[counter]).age);
    printf("high bp: "); scanf("%d", (*db[counter]).highBP);
    printf("low bp: "); scanf("%d", (*db[counter]).lowBP);


    //db[counter] = &temp;
    printf("%d", sizeof(db[counter]));
    //printf("%s", (db[counter])->name);
    printf("%s, %d, %f, %f\n", db[counter]->name, db[counter]->age, db[counter]->highBP, db[counter]->lowBP);
    counter++;*/
}

---

You do this:

scanf("%s",selectionstr); /* Leaves '\n' in the input buffer. */

And then you do the gets

gets(name); /* Encounters the leftover '\n'. */

The problem is that scanf doesn't consume the newline, which remains in the input buffer. When gets comes along, it encounters the newline and is immediately satisfied.

This question comes up often enough. It's also a C FAQ. And explained quite well here.

There are things to consider:

• Someone will propose "flushing stdin". This is a bad idea.

• Someone will propose something like

  while((c = getchar()) != '\n' && c != EOF);
  

  which is also troublesome

Your best bet is not to mix up scanf and gets.

As a side note, you do realize you should be using fgets instead of gets, right ?

---

Main Problems

Do not use gets(), ever. Not even in toy programs. It is a bad habit to get into. It cannot be used safely, ultimately, because you cannot tell when the input is going to overflow the buffer you provide.

Use fgets() instead, and remember to remove the trailing newline it leaves behind (the one gets() removes).

Your problem is that the previous input with scanf() didn't read the newline, so gets() reads to the first newline - giving you an empty string. You'd run into the same problem on the next iteration, too, because you read the blood pressure with scanf().

Auxilliary Problems

You do not check that the inputs succeeded; always check the return value from scanf() to ensure that you got the inputs you expected. You'd be getting errors because the name can't be interpreted as a number.

You should get into the habit of writing code that declares functions with prototypes; the notation:

void enter();

says "there is a function enter() that returns no value and takes an indeterminate argument list - any set of arguments is OK, but it isn't a variable argument list function". By contrast:

void enter(void);

says "there is a function enter() that returns no value and takes no arguments".

Also, you should explicitly define the return type of main() as int. It has been more than a decade since the C standard required explicit return types on all function definitions.

Incipient Problem

Once you get over the data scanning problem, you will find that you are not allocating space properly for your records. Your array is:

struct patient *db[RECORDS];

In the loop, you have:

struct patient temp;

db[counter] = &temp;

The troubles are two-fold. You are re-using the same space for each patient record, and the pointer you are storing goes out of scope when enter() exits. The simplest fix is to change the global variable to:

struct patient db[RECORDS];

You can then do away with the temp variable, and simply initialize the appropriate entry in db. Alternatively, you can keep temp but do structure assignment instead of pointer assignment:

db[counter] = temp;

---

The problem is that after the scanf-call, there's still a "\n" (or whatever newline is on your system) in the input buffer and when you call gets(), it fetches the newline and returns. What you need to do is to clear the input buffer. Like this, e.g.:

int c;
while ( ( c = getchar() ) != EOF && c != '\n' )
  ;

---

What used to be:

gets(str);

is now replaced by:

int c;
while ( (c = getchar()) != EOF && c != '\n' )
    ;
fgets(str, sizeof(str), stdin);
str[strlen(str) - 1] = '\0';

I hate this but this seems to be the minimal code that does what I need. And this is even assuming that the user hits 'enter' at the end of input. It's not robust!