C programming

Question

#include<string.h>
#include<stdio.h>
int main()
{
    char str[13]="C at lakshya";
    char str1[]="secret";
    strcat(str,str1);
    printf("%d %d",sizeof(str),strlen(str));
}

Output :- $13$ $18$

Here although sizeof str is $13$ then also it is concatenating why ?

Answer 1

Nice question. This is an undefined behavior. Because C doesn't do out of bounds checking, anything can happen when we try to read/write contiguously after the allocated memory of a predefined array.

Explained here in detail:

https://stackoverflow.com/a/30757295/8354936