The **`wcstoul`** function in C interprets a given wide string as an unsigned integral number of a specified base. All characters up to the first non-numeric character are converted to an `unsigned long integer`. The `wcstoul` function ignores any leading whitespace.

>Note: The `unsigned long` data type can take on any value between $0$ to $(2^{32}-1)$.

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

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

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

```C
unsigned long int wcstoul(const wchar_t *str, wchar_t **str_end, int base);
```

# Parameters

The `wcstoul` function takes the following objects as parameters:

* `str`: The wide string to be converted.
* `str_end`: A pointer that references the characters after the last valid numeric character in `str`. This parameter may also be a null pointer.
* `base`: The base of the integral value.

>Note: The set of values for the base is {$0$,$2$,$3$,...,$35$,$36$}.


# Return value

If the conversion is successful, the `wcstoul` function returns an `unsigned long integer` value; otherwise, it returns $0$.


# Example

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

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

int main() {

  // initilaizing strings
  wchar_t str[] = L"2021Educative22";
  wchar_t* str_end;
  unsigned long int result;

  // converting string to long long int
  result = wcstoul(str, &str_end, 10);

  // output results
  printf("The converted unsigned integral number is %lu.\n", result);
  printf("The remaining string is \'%ls\'.", str_end);
  
  return 0;
}

# Explanation

First, the code initializes the wide string we want to convert. The 'L' identifier in *line 7* informs the compiler that the Unicode character set is being used. The `str_end` pointer will contain the string that remains after conversion.

The `wcstoul` function in *line 12* proceeds to convert the given wide string, "2021Educative22", to an `unsigned long integer`. For this example, the decimal number system (base $10$) is used. 

Since the first $4$  characters ("2021") represent valid numeric characters, the conversion is successful and the `wcstoul` function returns the value **$2021$**. The remaining string, "Educative22", is stored at the location pointed to by `str_end`.

What is wcstoul in C?

Function wcstoul converts a wide string to an unsigned long integer based on the specified base, using the wchar.h library.