Thread: fgets is skipping the second time I call it

Hey C Board. I created a typedef structure called Student, and I want to pass this structure to two functions, getStudent, to scanf all the members, and printStudent, to print all the members.

Code:

#include <stdio.h>

typedef struct {
	char name[70];
	int age;
	double gpa;
} Student;

void getStudent(Student *s) {
	printf("Enter name: ");
	fgets(s->name, sizeof(s->name), stdin);
	printf("Enter age: ");
	scanf("%d", &s->age);
	printf("Enter GPA: ");
	scanf("%lf", &s->gpa);
}

void printStudent(Student *s) {
	printf("Name: %s", s->name);
	printf("Age: %d\n", s->age);
	printf("GPA: %.2f\n", s->gpa);
}

int main(void) {
	Student bill, jeff;
	getStudent(&bill);
	printf("\n");
	printStudent(&bill);
	printf("\n");
	getStudent(&jeff);
	printf("\n");
	printStudent(&jeff);
	return 0;
}

Here's the output. It completely skips the second time I call fgets. What am I doing wrong?

Code:

$ ./a.out
Enter name: James
Enter age: 20
Enter GPA: 3.4

Name: James
Age: 20
GPA: 3.40

Enter name: Enter age: 22
Enter GPA: 4.0

Name: 
Age: 22
GPA: 4.00

The scanf leaves the newline behind. Then the fgets reads only up to the newline, which is nothing.
If the name does not contain spaces, you could use scanf with "%s".
If the name can contain a space, then you could use scanf with "%[^\n]".

scanf("%[^\n]", s->name) does the same thing.

Originally Posted by Babkockdood

scanf("%[^\n]", s->name) does the same thing.

Oops. I forgot to mention that you should put a space before it.

Code:

scanf(" %[^\n]", s->name);

Originally Posted by oogabooga

Oops. I forgot to mention that you should put a space before it.

Code:

scanf(" %[^\n]", s->name);

That worked, thanks.

The problem with oogabooga's suggestions is that unless you also specify the field width, your code is vulnerable to buffer overflow. fgets does not have this problem since you specify the maximum number of characters to read as an argument.

laserlight is of course correct. And it turns out to be rather ugly to fix without hardcoding the buffer size in the format. Here's a possibility:

Code:

#include <stdio.h>

#define STR_SIZE 10
#define STRINGIZE(x)  STRINGIZE2(x)
#define STRINGIZE2(x) #x

int main(void) {
    char str[STR_SIZE+1]; // must add 1 here
    scanf(" %" STRINGIZE(STR_SIZE) "[^\n]", str);
    printf("<%s>\n", str);
    return 0;
}

But I should have mentioned that reading in lines with fgets and then dealing with them (with sscanf, atoi, etc) is the preferred method.