The **`wcslen`** function in C returns the number of characters in a wide string, excluding the null terminating character.

The process is illustrated below:

>Note: A `wide string` is comprised of characters from the [Unicode](https://unicodebook.readthedocs.io/programming_languages.html) character set.

To use the `wcslen` function, you will need to include the `<wchar.h>` library in the program, as shown below:

```C
#include <wchar.h>
```

The prototype of the `wcslen` function is shown below:

```C
size_t wcslen(const wchar_t *str);
```

# Parameters

The `wcslen` function takes a single parameter, i.e., a pointer to a null-terminated wide string.

# Return Value

The `wcslen` function returns the length of the given wide string, excluding the null-terminating character.

# Example

The code below shows how the `wcslen` function works in C:

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

int main() {

  // initializing wide string
  wchar_t str1[] = L"Hello World";
  wchar_t str2[] = L"Learn wcslen in C";

  // calculate lengths
  size_t len1 = wcslen(str1);
  size_t len2 = wcslen(str2);

  // output results
  printf("\'%ls\' contains %d characters.\n", str1, len1);
  printf("\'%ls\' contains %d characters.\n", str2, len2);
  
  return 0;
}

# Explanation

First, the code initializes two wide strings. The **'L'** identifier in `lines 7 and 8` informs the compiler that the Unicode character set is being used.

The `wcslen` function proceeds to find the length of both of these strings in `lines 11 and 12`, respectively. These lengths are then written to `stdout`. 

What is wcslen in C?

The wcslen function in C returns the length of a wide string excluding the null-terminating character.