FPDFText_FindStart findwhat in c++ is FPDF_WIDESTRING ，but in FPDFTextFindStart is ushort findwhat，i dont know How to convert?

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I found parameter “findwhat” in other projects define byte[] not “ref ushort findwhat”，Suggestions for other ways to do this?ths

// Function: FPDFText_FindStart
// Start a search.
// Parameters:
// text_page - Handle to a text page information structure.
// Returned by FPDFText_LoadPage function.
// findwhat - A unicode match pattern.
// flags - Option flags.
// start_index - Start from this character. -1 for end of the page.
// Return Value:
// A handle for the search context. FPDFText_FindClose must be called
// to release this handle.
//
FPDF_EXPORT FPDF_SCHHANDLE FPDF_CALLCONV
FPDFText_FindStart(FPDF_TEXTPAGE text_page,
FPDF_WIDESTRING findwhat,
unsigned long flags,
int start_index);

public static global::PDFiumCore.FpdfSchhandleT FPDFTextFindStart(global::PDFiumCore.FpdfTextpageT text_page, ref ushort findwhat, uint flags, int start_index)