SPI_fnumber — determine the column number for the specified column name
int SPI_fnumber(TupleDescrowdesc, const char *colname)
SPI_fnumber returns the column number for the column with the specified name.
If colname refers to a system column (e.g., ctid) then the appropriate negative column number will be returned. The caller should be careful to test the return value for exact equality to SPI_ERROR_NOATTRIBUTE to detect an error; testing the result for less than or equal to 0 is not correct unless system columns should be rejected.
TupleDesc rowdescinput row description
const char * colnamecolumn name
Column number (count starts at 1 for user-defined columns), or SPI_ERROR_NOATTRIBUTE if the named column was not found.