Why strcat is not working in this case?

This is throwing a runtime error

Code:

---

#include<studio.h>
#include<string.h>

int main()
{
const char *x="hello";
char *s=" world";
strcat(s,x);
return 0;
}

---

Because attempting to modify a string literal results in undefined behaviour, and you're doing just that by attempting to concatenate "hello" with the string literal " world". In fact, I told you in another thread:

Quote:

---

Originally Posted by laserlight

c should have been declared as a pointer to const char instead so as to avoid accidentally attempting to modify a string literal, which would result in undefined behaviour.

---

So why did you persist in declaring s to be a pointer to non-const char? You should have declared it to be a pointer to const char, and then your mistake would have become obvious.

Now even on changing the code tho this, once it had printed " worldhello" but rest of the times it said runtime error.

Code:

---

#include<studio.h>
#include<string.h>

int main()
{
const char x[]="hello";
char s[]=" world";
strcat(s,x);
printed("%s",s);
return 0;
}

---

As well as making sure you're trying to modify writeable memory, you also need to ensure you have enough memory to write to.

Code:

---

const char x[]="hello";
char s[]=" world";
strcat(s,x);

---

The compiler will measure the length of your string constants, and allocate just enough memory for s and x.

If you're trying to see "hello world", then your strcat parameters are the wrong way round.

Code:

---

char x[30]="hello";  // 30 chars, initialised to "hello\0\0\0\0<20 more \0>\0"
char s[]=" world";
strcat(x,s); // append s onto the end of x

---

Since "studio.h" and "printed" don't exist, how are you compiling this?

Code:

---

char x[6]="hello"; 
char s[]=" world";
strcat(x,s);

---

Despite not giving enough space to x this code is giving output as "hello world". Why?

> Despite not giving enough space to x this code is giving output as "hello world". Why?
Because of pure dumb luck.

I would suggest you learn how to do it properly, instead of experimenting with all sorts of undefined behaviour and wondering why various things do (or do not) happen.