The **`wcstod`** function in C interprets a given wide string as a floating-point number. All characters up to the first non-numeric character are converted to a `double`. The `wcstod` function ignores any leading whitespaces.

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

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

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

```C
double wcstod(const wchar_t *str, wchar_t **str_end);
```

# Parameters

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

* `str`: The wide string to be converted.
* `str_end`: A pointer to a wide character. The value of this pointer is set to the next character in `str` after the last valid floating-point character. This parameter may also be a null pointer.

# Return value

If the conversion is successful, the `wcstod` function returns a double value; otherwise, $0$ is returned.

If the converted value is out of range, the `wcstod` function returns a positive or negative [HUGE_VAL](https://learn.microsoft.com/en-us/cpp/c-runtime-library/huge-val-huge?view=msvc-160).

# Example

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

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

int main() {

  // initilaizing strings
  wchar_t str[] = L"2021.2Educative22";
  wchar_t* str_end;
  double result;

  // converting string to double
  result = wcstod(str, &str_end);

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

# Explanation

First, the wide string we want to convert is initialized. 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 `wcstod` function in Line 12 proceeds to convert the given wide string, "2021.2Educative22", to a `double`. 

Since the first $6$  characters ("2021.2") represent a valid floating-point number, the conversion is successful, and the `wcstod` function returns the value **$2021.2$**. The remaining string, "Educative22", is stored at the location pointed to by `str_end`.

What is wcstod in C?

Interprets a wide string as a double, ignoring leading whitespaces and converting up to the first non-numeric character.