Function names can be 'overloaded' in C++. Two functions with the same name can coexist if they have different arguments, as in:
int func( int i )
and
int func( char c )
C++ compilers 'type-decorate' or 'mangle' function names by default. This means that argument type names are appended to their function names to resolve them, as in func__Fi and func__Fc for the two earlier examples. The mangled names will be different on each platform, so code that explicitly uses a mangled name is not portable.
The type-decorated function name can be determined from the .o file (object file) or the shared library using the nm command. This command can produce considerable output, so we suggest you pipe the output through grep to look for the right line, as follows:
nm myprog.o | grep myfunc
where myprog.o is your program object file, and myfunc is the function in the program source file.
The output produced by the command includes a line similar to the following:
myfunc__FPlT1PsT3PcN35| 3792|unamex| | ...
When registering such a UDF with CREATE FUNCTION, the EXTERNAL NAME clause must specify the mangled function name obtained from nm:
CREATE FUNCTION myfunco(...) RETURNS...
...
EXTERNAL NAME '/whatever/path/myprog!myfunc__FPlT1PsT3PcN35'
...
Likewise, when calling a stored procedure, the function name also specifies the mangled function name:
CALL 'myprog!myfunc__FPlT1PsT3PcN35' ( ... )
If your stored procedure or UDF library does not contain overloaded C++ function names, you have the option of using extern "C" to force the compiler to not type-decorate function names. (Note that you can always overload the SQL function names given to UDFs, since DB2 resolves what library function to call based on the name and the parameters it takes.)
#include <string.h>
#include <stdlib.h>
#include "sqludf.h"
/*---------------------------------------------------------------------*/
/* function fold: output = input string is folded at point indicated */
/* by the second argument. */
/* inputs: CLOB, input string */
/* LONG position to fold on */
/* output: CLOB folded string */
/*---------------------------------------------------------------------*/
extern "C" void fold(
SQLUDF_CLOB *in1, /* input CLOB to fold */
...
...
}
/* end of UDF: fold */
/*---------------------------------------------------------------------*/
/* function find_vowel: */
/* returns the position of the first vowel. */
/* returns error if no vowel. */
/* defined as NOT NULL CALL */
/* inputs: VARCHAR(500) */
/* output: INTEGER */
/*---------------------------------------------------------------------*/
extern "C" void findvwl(
SQLUDF_VARCHAR *in, /* input smallint */
...
...
}
/* end of UDF: findvwl */
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In this example, the UDFs fold and findvwl are not type-decorated by the compiler, and should be registered in the CREATE FUNCTION statement using their plain names. Similarly, if a C++ stored procedure is coded with extern "C", its undecorated function name would be used in the CALL statement.