Malloc for structures

Question

I am not getting the correct output here, The code takes the no of inputs and option as an input, then takes the name of student year and gender and based on option provided gives the output. The output can be the name appearing first in the dictionary or the smaller value of the year amongst the inputs.

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

struct student_record
{
    int passing_year;
    char gender;
    char name[20];
};

typedef struct student_record student;

student* find_specific(student* find, int option_num, int number)
{
    int i;
    student* temp = find;
    int opt = option_num;
    int num = number;

    if(opt==1)
    {
        for(i=0; i<num; i++)
        {
            if( strcmp(temp->name, find[i].name) >0)
                temp = find+i;
        }
    }
    else
    {
        for(i=0; i<num; i++)
                {
                    if (temp->passing_year > find[i].passing_year)
                        temp = find+i;
                }
    }

    return temp;

}

int main() {

    student* example;
    student* final;

    int i;
    int option_num, number_of_students;
    printf("Enter 2the number of students, option number");
    scanf("%d" "%d", &number_of_students, &option_num);

    example = (student* )malloc(number_of_students * sizeof(student));

    printf("Enter the name, passing year and gender");
    for(i=0; i< number_of_students; i++)
    {

        scanf("%s" "%d" "%c", example[i].name, &example[i].passing_year, &example[i].gender);
    }

    final = find_specific(example, option_num, number_of_students);

    printf("%s" "%d" "%c", final->name, final->passing_year, final->gender );





    return 0;
}

i am getting a segmentation fault. I can't figure out exactly where am I screwing up.

"I can't figure out exactly where am I screwing up." - always run under a debugger when you're unsure what is going on, and it'll tell you. — Johann Gerell
– Johann Gerell, Commented Feb 16, 2015 at 2:01
I like how number is assigned to num just for the purpose of being used in the for loop... — thang
– thang, Commented Feb 16, 2015 at 2:16
Don't cast the return value of malloc() but, check that it's not NULL. — Iharob Al Asimi
– Iharob Al Asimi, Commented Feb 16, 2015 at 2:19

Iharob Al Asimi · Accepted Answer · 2015-02-16 02:19:05Z

3

Your scanf() and printf() format strings are probably wrong.

scanf("%s" "%d" "%c", example[i].name, &example[i].passing_year, &example[i].gender);

should probably be

scanf("%s %d %c", example[i].name, &example[i].passing_year, &example[i].gender);

(without the extra quotes). The compiler will concatenate adjacent string literals, so instead of a compiler error, it interpreted your format string as equivalent to "%s%d%c" (without whitespace in between). That probably doesn't match the layout of your input, so some of the values were probably left uninitialized in a way that caused problems later.

You should always check the return value of scanf and similar library functions, to ensure that you got the input format you told the compiler to expect.

edited Feb 16, 2015 at 2:19

Iharob Al Asimi

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answered Feb 16, 2015 at 2:06

Jim Lewis

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1 Comment

Iharob Al Asimi Over a year ago

The problem is that the "%c" specifier is matching the whitespace, to skip it you need to have a explicit whitespace before the "%c" specifier, hence "%s%d %c".

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