The **`tmpnam_s` function** is a C library function that creates a unique name for temporary files. The function generates a different filename each time we call the function, up to `TMP_MAX_S` times. The filenames should not be greater than `L_tmpnam_s` in length. 

> `TMP_MAX_S` and `L_tmpnam_s` are macros defined in the `stdio.h` header file. 

To use the `tmpnam_s` function, we need to include the `stdio.h` header file, as shown below:
```C
#include stdio.h
```

# Syntax 
The `tmpnam_s` function is declared as follows:

# Parameters
The `tmpnam_s` function takes the following two parameters:

* A `character pointer` that points to the array of characters. The filename is a C string. 

* The maximum number of characters the function is allowed to write. This value is of the `rsize_t` type.

# Return value
The `tmpnam_s` function returns a pointer to a C string that contains the valid filename: 

* If the parameter `filename_s` is a `NULL` pointer, the return value will point to the `tmpnam_s's` internal buffer, which the subsequent calls to the function will overwrite.

* If the parameter `maxsize` is greater than`RSIZE_MAX` macro, an error is generated.  

* If the parameter `maxsize` is less than the generated filename string, an error is generated.

* If the parameter `filename_s` is *not* `NULL`, the function returns the filename. A `NULL` pointer is returned in case a suitable filename is not found. 




# Example
The code below shows the use of the `tmpnam_s` in C. This function works the same way as the `tmpnam` function in C except for the extra safety checks. First, we call the function, and if an error is detected, we display the error message in line 16. If there are no errors, we display the filename in line 21:

> To find more information about the `tmpnam` function in C, [click here](https://www.educative.io/answers/what-is-tmpnam-in-c).

#include <stdio.h>
#include <stdlib.h>

int main( void )
{
  //Declare values 
  char filename[L_tmpnam_s];
  errno_t e;

  //Call the function 
  e = tmpnam_s(filename, L_tmpnam_s );
  
  //Display result 
  if (e) 
  {
    printf("Error occurred! \n");
  }
  
  else
  {
    printf( "Temporary filename: %s\n", filename );
  }

}

The filenames generated by the `tmpnam_s` function are random and difficult to guess. 

However, a sample output of the above code is as follows:

`Temporary filename: /tmp/fileRZHMwL`

tarball.tar.gz

What is tmpnam_s() in C?

Creates unique names for temporary files in C with safety checks, ensuring random and difficult-to-guess filenames.