The following example simply adds two scalars. Other examples can be found in subdirectories of $CEI/ensight251/src/math_functions/

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#ifndef WIN32 
#include <unistd.h> 
#endif  
#include "../extern/udmf_extern.h"  
/*-------------------------------------------------------------------- 
 * USERD_get_name_of_mf 
 *-------------------------------------------------------------------- 
 * 
 *   Gets the name of the math function, so gui can list as a calculator 
 *   function. 
 * 
 *  (OUT) mf_name          = the name of the math function 
 *                           (max length is UDMFSNAME, which is 64) 
 * 
 *  returns: Z_OK  if successful 
 *           Z_ERR if not successful 
 * 
 *--------------------------------------------------------------------*/ 
int 
USERD_get_name_of_mf(char mf_name[UDMFSNAME]) { 
  memset(mf_name,'\0',UDMFSNAME); 
  strcpy(mf_name, "addTwoScalars"); 
  return(Z_OK); 
}  
/*-------------------------------------------------------------------- 
 * USERD_get_mf_version 
 *-------------------------------------------------------------------- 
 * 
 *   Gets the version number of the user defined math function supported API 
 * 
 *  (OUT) version_number       = the version number of the math function 
 *                             (max length is UDMFSNAME, which is 64) 
 * 
 *  returns: Z_OK  if successful 
 *           Z_ERR if not successful 
 * 
 *  Notes: 
 *  * version needs to be "1.000". 
 *--------------------------------------------------------------------*/ 
int 
USERD_get_mf_version(char version_number[UDMFSNAME]) {  
  strcpy(version_number, "1.000"); 
  return(Z_OK); 
}  
/*-------------------------------------------------------------------- 
 * USERD_get_nargs 
 *-------------------------------------------------------------------- 
 * 
 *   Gets the number of arguments needed by the function. 
 * 
 *  (OUT) nArgs       = the number of arguments 
 * 
 *  returns: Z_OK  if successful 
 *           Z_ERR if not successful 
 * 
 *--------------------------------------------------------------------*/ 
int 
USERD_get_nargs(int *nArgs) {  
  *nArgs = 2; 
  return(Z_OK); 
}  
/*-------------------------------------------------------------------- 
 * USERD_get_meta_data 
 *-------------------------------------------------------------------- 
 * 
 *   Get the function descriptions, argument types, and return type.  
 * 
 *  (OUT) listDescription = description shown in general function column 
 *  (OUT) funcDescription = description shown in feedback window 
 *  (OUT) argTypes = data types of arguments passed into USERD_evaluate 
 *  (OUT) returnType = data type returned by function USERD_evaluate 
 * 
 *  returns: Z_OK  if successful 
 *           Z_ERR if not successful 
 * 
 *--------------------------------------------------------------------*/ 
int 
USERD_get_meta_data(char listDescription[UDMFLNAME], 
                    char funcDescription[UDMFLNAME], 
                    int *argTypes, int *returnType) {  
  strcpy(listDescription, "add2(part, scalar, scalar)");  
  strcpy(funcDescription, "add2(any part(s), scalar, scalar)");  
  argTypes[0] = UDMFSCL; 
  argTypes[1] = UDMFSCL;  
  *returnType = UDMFSCL;  
  return(Z_OK); 
}  
/*-------------------------------------------------------------------- 
 * USERD_evaluate 
 *-------------------------------------------------------------------- 
 * 
 *   Evaluate the function. 
 * 
 *  (OUT) args = pointers to arguments  
 *  (OUT) undefined = boolean; true if return value is undefined. 
 *  (OUT) value = returned value 
 * 
 *  returns: Z_OK  if successful 
 *           Z_ERR if not successful 
 * 
 *--------------------------------------------------------------------*/ 
int 
USERD_evaluate(void *args[], void *value, int *undefined) {  
  float *result; 
  float *arg1, *arg2;  
  result = value; 
  arg1 = args[0]; 
  arg2 = args[1];  
  *result = *arg1 + *arg2; 
  *undefined = 0;  
  return(Z_OK); 
}