SPI_execute_plan and vardata

Hello

I can't:convert char* to Datum

Datum Values[2];

Values[0]-is integer type 
but Values[1] is string type so 

Values[0] = SET_4_BYTES(227);

please assist how can i convert som char* string to Datum

Values[1] = CONVERT_STRING_TO DATUM(char *); etc

best
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Арсен Арутюнян