The **`wcsstr`** function looks for the first occurrence of a wide string 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?

Parameters

Return value

Example 1

Example 2