c program hangs when gets used in structure

Question

I am trying to learn structures and the below code is having some sort of error, not logical but just shows up while execution saying, the file has stopped working. Occurs right after gets(s2.name)

#include<stdio.h>
struct student
{
  char *name;
  float mark1,mark2,mark3;
  float total;
};
int main()
{
struct student s1,s2,s[3];
s1.mark1=6;s1.mark2=7;s1.mark3=8;
s1.total = s1.mark1+s1.mark2+s1.mark3;
printf("\nEnter the name of s2 : ");
gets(s2.name);
/*when above line is inserted program hangs and code below does not execute*/
puts(s2.name);
s1.name = "shanky";
puts(s1.name);
getch();
return 0;
}

No compilation error obviously. Using gcc compiler

Undefined behavior for using the value of an object with automatic storage duration while it is indeterminate. — EOF, Jan 14 '17 at 17:14
Good idea for one statement per line. i.e. ; -> start a new line — Ed Heal, Jan 14 '17 at 17:16
[DO NOT use `gets()`, it is dangerous](http://stackoverflow.com/q/1694036/2173917). use [`fgets()`](https://linux.die.net/man/3/fgets) instead. — Sourav Ghosh, Jan 14 '17 at 17:23
Are you familiar with GDB? It is immensely useful to know how to step a program through a debugger (just an FYI). — RastaJedi, Jan 14 '17 at 17:25
@shanky What kind of compiler are you using, and did you enable warnings? — EOF, Jan 14 '17 at 17:27
@EOF No. Warnings are disabled in gcc by default. I really missed something here — shanky, Jan 14 '17 at 17:37

score 4 · Answer 1 · answered Jan 14 '17 at 17:16

4

You forgot to allocate memory for the name member of the struct. It is a pointer, but unless you malloc() some memory, you have no idea where it points to.

Try something like s2.name = malloc(80). Make sure you check the return value, and note that gets() is unsafe. Don't use that in production code. (or rather, don't use gets() at all).

answered Jan 14 '17 at 17:16

Marc Balmer

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`but unless you malloc() some memory`..how about assigning a pointer to another statically allocated variable? – Sourav Ghosh Jan 14 '17 at 17:24
@SouravGhosh: that works for one structure variable; it rapidly becomes untenable when there's more than one variable of that type kicking around. – Jonathan Leffler Jan 14 '17 at 22:06

c program hangs when gets used in structure

1 Answers1