char * SPI_getvalue(HeapTuple row, TupleDesc rowdesc, int colnumber)
SPI_getvalue returns the string representation of the value of the specified column.
The result is returned in memory allocated using palloc. (You can use pfree to release the memory when you don't need it anymore.)
Column value, or NULL if the column is null, colnumber is out of range (SPI_result is set to SPI_ERROR_NOATTRIBUTE), or no no output function available (SPI_result is set to SPI_ERROR_NOOUTFUNC).