The **`wcsstr`** function looks for the first occurrence of a [wide string](https://www-user.tu-chemnitz.de/~heha/petzold/ch02c.htm) in another wide string. It is defined in the `<wchar.h>` header file.

# Parameters
```C
wchar_t* wcsstr(wchar_t* haystack, wchar_t* needle);
```
In the above snippet of code, both `haystack` and `needle` are pointers to two separate wide strings. When we call the function, the first occurrence of `needle` is searched in `haystack`.

# Return value
If `needle` is found in `haystack`, a pointer to its first occurrence is returned. 
Else, `NULL` is returned.  

If `needle` is empty, a pointer to the beginning of `haystack` is returned.

As shown in the figure above, the pointer returned from the function points to the beginning of first occurrence of `needle` in `haystack`. The code for the above drawn figure is written below:

# Example 1

#include<stdio.h>
#include<wchar.h>

void main() {
  
  // declaring and initializing strings of wide characters 
  wchar_t haystack[] = L"HELLOWORLD!";
  wchar_t needle[] = L"LLO";

  // calling the function and storing the returned value in a pointer
  wchar_t* returnedPtr = wcsstr(haystack, needle);

  // checking if the substring was found
  if(returnedPtr == NULL) {
    printf("SUBSTRING NOT FOUND \n");
  }
  else {
    // printing the returned string/pointer
    wprintf(L"%ls", returnedPtr);
  }
  
}

In the above snippet of code, we are searching for the substring *LLO* in the string *HELLOWORLD*. The `returnedPtr` pointer points to the first *L* in the string `haystack`. Due to this, when we call the `wprintf` function on the returned pointer, it prints from the first *L* till the end of `haystack`.

>Note that we used `L` prefix while declaring and initializing wide strings and  `wprintf` function to print a wide string.

# Example 2

#include<stdio.h>
#include<wchar.h>

void main() {
  
  // declaring and initializing strings of wide characters 
  wchar_t haystack[] = L"HELLOWORLD!";
  wchar_t needle[] = L"";

  // calling the function and storing the returned value in a pointer
  wchar_t* returnedPtr = wcsstr(haystack, needle);

  // checking if the substring was found
  if(returnedPtr == NULL) {
    printf("SUBSTRING NOT FOUND \n");
  }
  else {
    // printing the returned string/pointer
    wprintf(L"%ls", returnedPtr);
  }
  
}

As shown in the above code snippet, the `wcsstr` function returns a pointer to the beginning of `haystack` if `needle` is empty.

What is wcsstr in C?

The wcsstr function looks for the first occurrence of a wide string in another wide string. It is defined in the  header file. Parameters wchar_t* wcsstr(wchar_t* haystack, wchar_t* needle);  In the above snippet of code, both haystack and needle are pointers to two separate wide strings. When we call the function, the first occurrence of needle is searched in haystack. Return value If needle is found in haystack, a pointer to its first occurrence is returned. Else, NULL is returned. If needle is empty, a pointer to the beginning of haystack is returned. 