why gets() is skip values inputs?

Question

I have struct:

typedef struct _client
{
    char num[9];    
    char some[12];  
} person;

and I want enter values to that strings, I have that code and in the iteration its skip for the first input and go to the second one. why it skip from input to the num[9] string and goes to the some[12]?

int i;
person* arrClient = (person*)malloc(sizeof(person)*size);
for (i = 1; i <= size; i++)
{
    gets(arrClient[i].num);
    gets(arrClient[i].some);
}

[Why is the gets function so dangerous that it should not be used?](https://stackoverflow.com/q/1694036/6865932) — anastaciu, Jun 06 '20 at 21:46
What is the input you provide? Do you input more characters than your buffer size allows? — Gerhardh, Jun 06 '20 at 21:46
Your loop range is invalid. In C array indexes start at `0` and go up to `size-1`. You mustn't access `arrClient[size]`. — Gerhardh, Jun 06 '20 at 21:47
"I input numbers" isn't enough information. What *exactly* is the input you provide? And you need to read the link in the first comment. Figuring out why a program with `gets` doesn't work may not be a good use of your time. Fix the program so it doesn't use `gets`. — Keith Thompson, Jun 06 '20 at 23:07

score 0 · Answer 1 · answered Jun 06 '20 at 22:42

Acessing an array ouside it's bounds leads to undefined behavior.

The cycle for (i = 1; i <= size; i++) does just that, replace it with for (i = 0; i < size; i++).

gets() function is no longer part of C standard, it was removed since ISO C11 because of its vulnerability:

The first internet worm (the Morris Internet Worm) escaped about 30 years ago (1988-11-02), and it used gets() and a buffer overflow as one of its methods of propagating from system to system. The basic problem is that the function doesn't know how big the buffer is, so it continues reading until it finds a newline or encounters EOF, and may overflow the bounds of the buffer it was given.

So use:

fgets(arrClient[i].num, sizeof(arrClient[i].num), stdin);
arrClient[i].num[strcspn(arrClient[i].num, "\n")] = '\0'; //remove '\n'

The same for the second input.

why gets() is skip values inputs?

1 Answers1