C – Passing argv[x] to Function as wchar_t

I’m trying to write some code that uses hidapi to do with some USB lights. The function within hidapi expects the serial_number to be passed as wchar_t, however my argv[] are char*

The way it DOES work is to hard code the SERIALNUMBER and use wcsncpy()

wcsncpy(serial_number, L"SERIALNUMBER", MAX_STR);
dev = hid_open(0x046d, 0xc900, serial_number);

The way it does NOT work is to send the serial number as a CLI argument (e.g. ./script SERIALNUMBER), after using a function to convert the char* to a wchar_t:

void ctow(char *toConvert, wchar_t *wstr) {
    int count = 0;
    int len = strlen(toConvert);
    for(; count < len; count++) {
        wstr[count] = (wchar_t) toConvert[count];
    }
}

What’s weird is that when you wprintf() the serial number it does come out correctly. I also noticed that if you don’t add the L to the hard coded serial number it also doesn’t work.

This is part of a much larger program, but I’ve whittled it down to just the immediate use case for troubleshooting. What am I doing wrong, here? Here is the full code:

#include <string.h>
#include <hidapi.h>

#define MAX_STR 255

void ctow(char *toConvert, wchar_t *wstr) {
    int count = 0;
    int len = strlen(toConvert);
    for(; count < len; count++) {
        wstr[count] = (wchar_t) toConvert[count];
    }
}

int main(int argc, char* argv[])
{
    wchar_t wstr[MAX_STR];
    wchar_t serial_number[MAX_STR];
    hid_device *dev;

    // ctow(argv[1],serial_number);                     // this DOES NOT WORK
    
    wcsncpy(serial_number, L"SERIALNUMBER", MAX_STR);   // this DOES work

    dev = hid_open(0x046d, 0xc900, serial_number);
    if (!dev) {
        wprintf(L"Open FAILED on serial number %ls", serial_number);
    }
    else {
        wprintf(L"Open SUCCESS on serial number %ls", serial_number);
    }
    return 0;
}

>Solution :

Use mbstowcs

char* foo = "abcdef";
wchar_t *wfoo = malloc((strlen(foo) + 1) * sizeof(wchar_t));
mbstowcs(wfoo, foo, strlen(foo) + 1);

see en.cppreference.com/w/c/string/multibyte/mbstowcs