Segmentation fault (core dumped)

Question

Below is a block of code from my program. I'm getting error of Segmentation fault (core dumped) after entering name and age in first loop.

#include<stdio.h>
#include <string.h>
struct Cricketer
{
    char name[25];
    int age;
    float avg_run;
};

int main(){
struct Cricketer c[3];
int i,j;

for (i=0 ; i<3;i++){
    printf("Enter name: \n");
    scanf("%s",c[i].name);

    printf("Enter age: \n");
    scanf("%d",c[i].age);

    printf("Enter average run: \n");
    scanf("%f",c[i].avg_run);               
}
return 0;
}

And I couldn't find what is causing this program.

No it's not `gcc` (the *compiler*) that crashes. It's your program that does when you run it. As for how to solve it, you first use a debugger to locate where in the program it happens. Please read [How to debug small programs](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/) by Eric Lippert. — Some programmer dude, Jul 27 '17 at 08:03
So is your question "How do you debug a core dump?" If so, you should state your platform and/or your preferred debugger. — David Schwartz, Jul 27 '17 at 08:06
Compile with all warnings & debug info: `gcc -Wall -Wextra -g`. Then **use the debugger `gdb`** . You fix-my-code question is off-topic. — Basile Starynkevitch, Jul 27 '17 at 08:11
A good compiler will warn you about the problem. If you don't have enough warnings enabled, or don't have a good enough compiler, fix it (add the warning options, or upgrade the compiler). — Jonathan Leffler, Jul 27 '17 at 08:12
@BasileStarynkevitch - too bad I can only vote once on a comment -- that reason, and that reason alone, enabling *Compiler Warnings* would probably resolve 50+% of the questions posted related to C. — David C. Rankin, Jul 27 '17 at 09:51

Jesferman · Answer 1 · 2017-07-27T09:40:42.897

2

Your error is here:

scanf("%d",c[i].age);

Change it for:

scanf("%d",&(c[i].age));

When using %d you have to pass the address of the int variable. And the same for floats:

scanf("%f",&(c[i].avg_run));

When using scanf, the second argument has to be the address of a variable. With your variable name there is no problem because it already refers to the address of the buffer in which you want to store the string.

edited Jul 27 '17 at 09:40

answered Jul 27 '17 at 08:02

Jesferman

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And the same for `c[i].avg_run` – vasek Jul 27 '17 at 08:03
Does it goes same for `name` also ? – Zachary Dale Jul 27 '17 at 08:04
No, for `name` is correct – Jesferman Jul 27 '17 at 08:05
@Jesferman Please tell him why it is correct for name and not for other fields... – Jean-Baptiste Yunès Jul 27 '17 at 08:09
1

Why the extraneous parentheses in `&(c[i].age)` instead of the simpler `&c[i].age`? – Jonathan Leffler Jul 27 '17 at 08:11
@JonathanLeffler only for clarifying the OP we are refering to the address of the variable and not the struct – Jesferman Jul 27 '17 at 08:13
I'd be OK with the parentheses if there was a comment about "or, in more idiomatic C, `&c[i].age`" or something along those lines. Showing the parenthesized version as the only solution isn't so good. – Jonathan Leffler Jul 27 '17 at 08:15
*Your error is here:* but that line is not even there in the original code. That is not his error, that is the correction. Please rephrase – Ajay Brahmakshatriya Jul 27 '17 at 09:37
@AjayBrahmakshatriya corrected. Thanks for your suggestion – Jesferman Jul 27 '17 at 09:42
@Jesferman - just a note that the parens are for emphasis only, as by C *Operator Precedence Rules* gives higher precedence to both `[ ]` and `'.'` making the parens unnecessary. – David C. Rankin Jul 27 '17 at 09:49
@DavidC.Rankin yes, i put them only for clarifying the OP we are refering to the address of the variable and not the struct – Jesferman Jul 27 '17 at 09:52
Yes, that's fair. Remember as you go farther here on S.O., you are stepping into the role of a teacher, helping to pass knowledge and learning along to the next generation of programmers, so you want to do as good a job as possible (and within reason) to discuss nuances of that particular area of code. Look forward to seeing many more of your answers here. – David C. Rankin Jul 27 '17 at 09:56
@DavidC.Rankin Thanks for help me to improve. Nice to meet kind people here – Jesferman Jul 27 '17 at 09:59

score 1 · Answer 2 · edited Sep 09 '17 at 20:41

1

When using scanf, the second argument should be the address of a variable. In your program c[i].age and c[i].avg_run are the variables themselves and not the addresses. Use the & operator to get the address of a variable. For Example, &(c[i].age) or just &c[i].age.

What you are passing to scanf as mentioned above are some numbers which might or might not be valid memory addresses. Thus invoking undefined behavior.

c[i].name happens to be fine because referring to an array (name in this case) by just the name evaluates to the base address of the array.

It is a good idea to have compiler warnings enabled. More important is one reads and understands the warnings. Read your compiler manual for more info.

edited Sep 09 '17 at 20:41

Jonathan Leffler

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answered Jul 27 '17 at 08:07

babon

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Why the extraneous parentheses in `&(c[i].age)` instead of the simpler `&c[i].age`? – Jonathan Leffler Jul 27 '17 at 08:13
@JonathanLeffler :) I can never remember the precedence rules. – babon Jul 27 '17 at 08:14
extra parenthesis are optional, you can use &c[i].age too and the result will be same. – Yatendra Rathore Jul 27 '17 at 08:21

Segmentation fault (core dumped)

2 Answers2