<h2>Overview</h2>

To understand the **`wctomb_s()`** function, you first need to understand the following terms:

1. **`wide character`**: A data type similar to the `char` data type in C. While `char` takes up 1-byte memory and represents only $2^8 = 256$ values, the wide character can take up to $65, 536$ (2 bytes) corresponding to UNICODE values. 

2. **multibyte encoding**: As there is a need to ensure that more characters can be encoded, we use varying number of bytes to encode a character. While the first byte ensures backward compatability, the rest can be used for representation beyond $256$ characters.

The `wctomb_s()` function, similar to the `wctomb()` function, converts the `wide character` variable `wc` to multibyte encoding. It is stored in the array pointed to by the variable `s`. `wctomb_s()` is defined in the `<stdlib.h>` header file, so it is important to include the library at the beginning of your code as shown below:

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

The `wctomb_s()` function is defined as the following in the `<stdlib.h>` library:

```C
errno_t wctomb_s(
   int *pRetValue,
   char *mbchar,
   size_t sizeInBytes,
   wchar_t wchar
);
```

<h2>Parameters</h2>

The `wctomb_s()` function requires 4 parameters:

1. `pRetValue`: a pointer to where the output will be stored. 
2. `mbchar`: a character array that points to the output of the multibyte encoding.
3. `sizeInBytes`: the size of the array `mbchar`, meaning the maximum bytes to be written to `mbchar`. `sizeInBytes` can never be greater than `MB_CUR_MAX`, which is the maximum number of bytes needed to represent a multibyte character for your machine. 
4. `wchar`: the wide character you need to convert to multibyte encoding. 

<h2>Return value</h2>

The return data type for the `wctomb_s()` function is `errno_t`. `errno_t` detects whether the function returns any errors. The following table represents each of the values that can be returned and what they mean:



align-center

If the `wctomb_s()` function is executed successfully, then the multibyte encoding will be stored in `s`, and `status` will store the length of the multibyte encoding. On the other hand, an error could also occur for the following reasons:

1. If `mbchar` is NULL but `sizeInBytes` is greater than zero.
2. If `sizeInBytes` is either too big or too small. 

<h2>Example</h2>

The example below shows how you can use the `wctomb_s()` function:


#include <stdio.h>
#include <stdlib.h>

int main()
{
    int i;
    wchar_t wide_char = L'C';

    char *output = (char *)malloc( MB_CUR_MAX );

    printf( "Converting a wide character to multibyte encoidng:\n" );
    wctomb_s( &i, output, MB_CUR_MAX, wide_char );
    printf( "Multibyte character output: %.1s\n", output );
    return 0;
}

<h2>Explanation</h2>

> Note: `L` is a prefix for wide character data type.

The `wctomb_s()` function converts the character 'C' to its multibyte encoding and prints it. 

The function above is not supported by the GCC compiler, so you will get an `implicit declaration of function…` error. Use the following variant to get the job done: 

```C
int wctomb (char* pmb, wchar_t wc);
```

Value	Meaning
0	Successful execution
Non-zero	Encoding error or runtime constraint violation

What is wctomb_s in C?

Overview

Parameters

Return value

Example

Explanation