UDF implementation of Dameng database

The official introduction is very simple , Actually, it's a little pit

Header file reference

//-I/dm/dmdbms/include/
#include "de_pub.h"

Library file reference

-L/dm/dmdbms/bin/ -ldmde

String splicing code ( Function names must be uppercase , Otherwise, the creation succeeds , Call error 【[-7095]: Failed to load external function .】)

de_data C_CONCAT(de_args *args)        
{
	de_data  de_ret;
	char* str1;
	char* str2;
	char* str3;
	int len1;
	int len2;

	str1 = (char*)de_get_str(args, 0);					 /* Take the... From the parameter list 0 Parameters */
	str2 = (char*)de_get_str_with_len(args, 1, (udint4*)&len2); 		 /* Take the... From the parameter list 1 The value and length of the parameters */
	len1 = strlen(str1);	
	str3 = (char*)malloc(len1 + len2);
	memcpy(str3, str1, len1);
	memcpy(str3 + len1, str2, len2);
	
	de_str_free((sdbyte*)str1); 	/* call get Function gets the string , You need to call this function to free the string space */
	de_str_free((sdbyte*)str2);
	
	de_ret = de_return_str_with_len((udbyte*)str3, len1 + len2);     /* Return string */
	free(str3); 
	return de_ret;
}

Build dynamic library

Create a function

CREATE OR REPLACE FUNCTION C_CONCAT(A VARCHAR, B VARCHAR) 
RETURN VARCHAR
EXTERNAL '/dm/dmdbms/bin/libtestudf.so' C_CONCAT USING C;
/

Actual project use

 

notes : because c Write Dameng udf Is take the dmap agent (/dm/dmdbms/bin/dmap), So you need to start the agent first . If the library depends on external environment variables , You need to start it manually on the console that configures the environment variables dmap, Instead of running disql Command line console configuration , Otherwise, environment variables cannot be recognized normally .