In this article Barry Mavin, CEO and Chief Software Architect for Recital details how to Build C Extension Libraries to use with Recital.

Overview

It is possible to extend the functionaliy of Recital products using "Extension libraries" that can be written in C. These extension libraries, written using the Recital/SDK API, are dynamically loadable from all Recital 9 products. This includes:

• Recital
• Recital Server
• Recital Web

Building C Extension Libraries

You can create C wrappers for virtually any native operating system function and access these from the Recital 4GL. Unlike traditional APIs which only handle the development of C functions that are callable from the 4GL, the Recital/SDK allows you to build Classes that are accessible from all Recital products. e.g. You could create a GUI framework for Linux that handles VFP system classes!

To deploy your C Extension Libraries, copy them to the following location:

Windows:

\Program Files\Recital\extensions

Linux/Unix:

/opt/recital/extensions

Please see the Recital/SDK API Reference documentation for further details.

Sample code

Listed below is the complete example of a C Extension Library.:

////////////////////////////////////////////////////////////////////////////////
#include "mirage_demo.h"  
      
////////////////////////////////////////////////////////////////////////////////
// Declare your functions and classes below as follows:
//
//    Recital Function Name, C Function Name, Type (Function or Class)
//
#define MAX_ELEMENTS    7
static  struct  API_SHARED_FUNCTION_TABLE api_function_table[MAX_ELEMENTS] = {
        {"schar",   "fnSamplesCharacter",   API_FUNCTION},
        {"stype",   "fnSamplesType",           API_FUNCTION},
        {"slog",    "fnSamplesLogical",        API_FUNCTION},
        {"snum",    "fnSamplesNumeric",    API_FUNCTION},
        {"sopen",   "fnSamplesOpen",         API_FUNCTION},
        {"myclass", "clsMyClass",               API_CLASS},
        {NULL,      NULL,                   -1}
};

////////////////////////////////////////////////////////////////////////////////
// Recital API initialization. This should be in only ONE of your C files
// **IT SHOULD NEVER BE EDITED OR REMOVED**  
INIT_API;


///////////////////////////////////////////////////////////////////////
// This is an example of passing a character parameter and returning one.
RECITAL_FUNCTION fnSamplesCharacter(void)
{
    char    *arg1;
    
    if (!_parse_parameters(PCOUNT, "C", &arg1)) { 
        ERROR(-1, "Incorrect parameters");
    }
    
    _retc(arg1);
}


///////////////////////////////////////////////////////////////////////
// This is an example of passing a numeric parameter and returning one.
RECITAL_FUNCTION fnSamplesNumeric(void)
{
    int arg1;
    
    if (!_parse_parameters(PCOUNT, "N", &arg1)) { 
        ERROR(-1, "Incorrect parameters");
    }
    
    _retni(arg1);
}


///////////////////////////////////////////////////////////////////////
// This is an example returns the data type of the parameter passed.
RECITAL_FUNCTION fnSamplesType(void)
{
    char    result[10];

    if (PCOUNT != 1) { 
        ERROR(-1, "Incorrect parameters");
    }
    
    switch (_parinfo(1)) {
        case API_CTYPE:
            strcpy(result, "Character");
            break;
        case API_NTYPE:
            strcpy(result, "Numeric");
            break;
        case API_LTYPE:
            strcpy(result, "Logical");
            break;
        case API_DTYPE:
            strcpy(result, "Date");
            break;
        case API_TTYPE:
            strcpy(result, "DateTime");
            break;
        case API_YTYPE:
            strcpy(result, "Currency");
            break;
        case API_ATYPE:
            strcpy(result, "Array");
            break;
        default:
            strcpy(result, "Unkown");
            break;
    }

    _retc(result);
}


///////////////////////////////////////////////////////////////////////
// This is an example returns "True" or False.
RECITAL_FUNCTION  fnSamplesLogical(void)
{
    char    result[10];
    int     arg1;
    
    if (!_parse_parameters(PCOUNT, "L", &arg1)) { 
        ERROR(-1, "Incorrect parameters");
    }
    
    if (arg1) strcpy(result, "True");
    else strcpy(result, "False");

    _retc(result);
}


///////////////////////////////////////////////////////////////////////
// This example opens a table.
RECITAL_FUNCTION fnSamplesOpen(void)
{
    char    *arg1;
    
    if (!_parse_parameters(PCOUNT, "C", &arg1)) { 
        ERROR(-1, "Incorrect parameters");
    }
    
    if (_parinfo(1) == API_CTYPE) {
        _retni(COMMAND(arg1));
    } else {
        _retni(-1);
    }
}

///////////////////////////////////////////////////////////////////////
// Define the MyClass CLASS using the API macros
///////////////////////////////////////////////////////////////////////
RECITAL_EXPORT int DEFINE_CLASS(clsMyClass)
{
    /*-------------------------------------*/ 
    /* Dispatch factory methods and return */
    /*-------------------------------------*/
    DISPATCH_FACTORY();
 
    /*---------------------------------*/
    /* Dispatch constructor and return */ 
    /*---------------------------------*/ 
    DISPATCH_METHOD(clsMyClass, Constructor);

    /*--------------------------------*/
    /* Dispatch destructor and return */
    /*--------------------------------*/
    DISPATCH_METHOD(clsMyClass, Destructor); 

    /*-----------------------------------*/
    /* Dispatch DEFINE method and return */
    /*-----------------------------------*/
    DISPATCH_METHOD(clsMyClass, Define);

    /*------------------------------*/
    /* Dispatch SET or GET PROPERTY */
    /* method for property NumValue */
    /* then return.                 */
    /*------------------------------*/
    DISPATCH_PROPSET(clsMyClass, NumValue);
    DISPATCH_PROPGET(clsMyClass, NumValue); 

    /*------------------------------*/
    /* Dispatch SET or GET PROPERTY */
    /* method for property LogValue */
    /* then return.                 */
    /*------------------------------*/
    DISPATCH_PROPSET(clsMyClass, LogValue);
    DISPATCH_PROPGET(clsMyClass, LogValue);

    /*-------------------------------*/
    /* Dispatch SET or GET PROPERTY  */
    /* method for property DateValue */
    /* then return.                 */
    /*-------------------------------*/
    DISPATCH_PROPSET(clsMyClass, DateValue);
    DISPATCH_PROPGET(clsMyClass, DateValue);

    /*-------------------------------*/
    /* Dispatch SET or GET PROPERTY  */
    /* method for property TimeValue */
    /* then return.                  */
    /*-------------------------------*/
    DISPATCH_PROPSET(clsMyClass, TimeValue);
    DISPATCH_PROPGET(clsMyClass, TimeValue);
 
    /*-------------------------------*/
    /* Dispatch SET or GET PROPERTY  */
    /* method for property CurrValue */
    /* then return.                  */
    /*-------------------------------*/
    DISPATCH_PROPSET(clsMyClass, CurrValue);
    DISPATCH_PROPGET(clsMyClass, CurrValue);

    /*-------------------------------*/
    /* Dispatch SET or GET PROPERTY  */
    /* method for property CharValue */
    /* then return.                  */
    /*-------------------------------*/
    DISPATCH_PROPSET(clsMyClass, CharValue); 
    DISPATCH_PROPGET(clsMyClass, CharValue);

    /*------------------------------*/
    /* Dispatch SET or GET PROPERTY */ 
    /* method for property ObjValue */ 
    /* then return.                 */
    /*------------------------------*/
    DISPATCH_PROPSET(clsMyClass, ObjValue);
    DISPATCH_PROPGET(clsMyClass, ObjValue);

    /*-----------------------------------*/
    /* If message not found return error */
    /*-----------------------------------*/
    OBJECT_RETERROR("Unknown message type");
}

////////////////////////////////////////////////////////////////////////////////
// Define METHOD handlers
////////////////////////////////////////////////////////////////////////////////
DEFINE_METHOD(clsMyClass, Constructor) 
{
        struct example_data *objectDataArea;

        /* Allocate memory for objects objectData area */
        objectDataArea = (struct example_data *) 
           malloc(sizeof(struct example_data));
        if (objectDataArea == NULL) return(-1);
    
        /* Assign the default property values */
        strcpy(objectDataArea->prop_charvalue, "Test API object");
        objectDataArea->prop_numvalue = 15.2827;
        objectDataArea->prop_logvalue = 'F';
        strcpy(objectDataArea->prop_datevalue, DATE_DATE());
        strcpy(objectDataArea->prop_timevalue, DATE_DATETIME());
        strcpy(objectDataArea->prop_currvalue, "15.2827");
        strcpy(objectDataArea->object_name, "APIobject");
        objectDataArea->prop_objvalue 
             = OBJECT_NEW(objectDataArea->object_name, "exception", NULL);
    
        /* Set the object objectData area */
        OBJECT_SETDATA((char *)objectDataArea);
    
        return(0);
}
  
DEFINE_METHOD(clsMyClass, Destructor) 
{
        struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();

        if (objectData != NULL) {
            if (objectData->prop_objvalue != NULL) 
              OBJECT_DELETE(objectData->prop_objvalue);
            free(objectData);
            objectData = NULL;
        }
        return(0);
}

DEFINE_METHOD(clsMyClass, Define) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();
    struct      API_EXPRESSION result;
    char        buffer[512];
    int         rc;

/* Check the object class */
    OBJECT_GETPROPERTY(objectData->prop_objvalue, "class", buffer);
    rc = OBJECT_GETARG(buffer, &result);
    if (result.errno == 0 && result.type == 'C' 
        && strcmp(result.character, "Exception") == 0) { 
        switch (OBJECT_GETARGC()) {
            case 1: 
                rc = OBJECT_GETPARAMETER(1, &result);
                if (result.errno == 0 && result.type == 'C') {
                    OBJECT_SETARG(buffer, &result);
                    rc = OBJECT_SETPROPERTY(objectData->prop_objvalue,
                         "message", buffer);
                }
                break;
            case 2: 
                rc = OBJECT_GETPARAMETER(2, &result);
                if (result.errno == 0 && result.type == 'N') {
                    OBJECT_SETARG(buffer, &result);
                    rc = OBJECT_SETPROPERTY(objectData->prop_objvalue,
                         "errorno", buffer);
                }
         }
    }

    result.type = 'L';
    result.logical = (rc == 0 ? 'T' : 'F');  
    OBJECT_RETRESULT(&result);
}

////////////////////////////////////////////////////////////////////////////////
// Define GET property handlers
////////////////////////////////////////////////////////////////////////////////
DEFINE_PROPERTYGET(clsMyClass, NumValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();

    if (objectData == NULL) return(-1);

    OBJECT_RETPROPERTY('N', objectData->prop_numvalue);
}

DEFINE_PROPERTYGET(clsMyClass, LogValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();

    if (objectData == NULL) return(-1);

    OBJECT_RETPROPERTY('L', objectData->prop_logvalue);
}  

DEFINE_PROPERTYGET(clsMyClass, DateValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();

    if (objectData == NULL) return(-1);

    OBJECT_RETPROPERTY('D', objectData->prop_datevalue);
}

DEFINE_PROPERTYGET(clsMyClass, TimeValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();

    if (objectData == NULL) return(-1);

    OBJECT_RETPROPERTY('T', objectData->prop_timevalue);
}

DEFINE_PROPERTYGET(clsMyClass, CurrValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();

    if (objectData == NULL) return(-1);

    OBJECT_RETPROPERTY('Y', objectData->prop_currvalue);
}

DEFINE_PROPERTYGET(clsMyClass, CharValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();

    if (objectData == NULL) return(-1);

    OBJECT_RETPROPERTY('C', objectData->prop_charvalue);
}

DEFINE_PROPERTYGET(clsMyClass, ObjValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();

    if (objectData == NULL) return(-1);

    OBJECT_RETPROPERTY('O', objectData->prop_objvalue);
} 


////////////////////////////////////////////////////////////////////////////////
// Define SET property handlers
////////////////////////////////////////////////////////////////////////////////
DEFINE_PROPERTYSET(clsMyClass, NumValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();
    struct API_EXPRESSION result;
    int rc = OBJECT_ERROR;

    OBJECT_GETVALUE(&result);
    if (result.errno == 0 && result.type == 'N') {
        objectData->prop_numvalue = result.number;
        rc = OBJECT_SUCCESS;
    }

    return(rc);
}

DEFINE_PROPERTYSET(clsMyClass, LogValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();
    struct API_EXPRESSION result;
    int rc = OBJECT_ERROR;

    OBJECT_GETVALUE(&result);
    if (result.errno == 0 && result.type == 'L') {
        objectData->prop_logvalue = result.logical;
        rc = OBJECT_SUCCESS;
    }

    return(rc);
}

DEFINE_PROPERTYSET(clsMyClass, DateValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();
    struct API_EXPRESSION result;
    int rc = OBJECT_ERROR;
    OBJECT_GETVALUE(&result);
    if (result.errno == 0 && result.type == 'D') {
        strcpy(objectData->prop_datevalue, DATE_DTOS(result.date));
        rc = OBJECT_SUCCESS;
    }

    return(rc);
}

DEFINE_PROPERTYSET(clsMyClass, TimeValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();
    struct API_EXPRESSION result;
    int rc = OBJECT_ERROR;

    OBJECT_GETVALUE(&result);
    if (result.errno == 0 && result.type == 'T') {
        strcpy(objectData->prop_timevalue, DATE_TTOS(result.datetime));
        rc = OBJECT_SUCCESS;
    }

    return(rc); 
}

DEFINE_PROPERTYSET(clsMyClass, CurrValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();
    struct API_EXPRESSION result;
    int rc = OBJECT_ERROR;

    OBJECT_GETVALUE(&result);
    if (result.errno == 0 && result.type == 'Y') {
        strcpy(objectData->prop_currvalue, CURR_YTOS(result.currency));
        rc = OBJECT_SUCCESS;
    }

    return(rc);
}

DEFINE_PROPERTYSET(clsMyClass, CharValue)  
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();
    struct API_EXPRESSION result;
    int rc = OBJECT_ERROR;

    OBJECT_GETVALUE(&result);
    if (result.errno == 0 && result.type == 'C') {
        strcpy(objectData->prop_currvalue, result.character);
        rc = OBJECT_SUCCESS;
    }

    return(rc);
}

DEFINE_PROPERTYSET(clsMyClass, ObjValue) 
{
    struct example_data *objectData = (struct example_data *)OBJECT_GETDATA();
    OBJECT  objvalue;
    int rc = OBJECT_ERROR;

    if (OBJECT_GETTYPE() == 'O') {
        objvalue = OBJECT_GETOBJECT(); 
        objectData->prop_objvalue = OBJECT_ASSIGN(objvalue, objectData->object_name);
        rc = OBJECT_SUCCESS;
    }

    return(rc);
}

Recital 10 introduced a FOREACH command, much like PHP and some other languages. This simply gives an easy way to iterate over arrays. foreach works on arrays and objects, and will issue an error when you try to use it on a variable with a different data type or an uninitialized variable. There are two syntaxes; the second is a minor but useful extension of the first:

FOREACH array_expression AS value
    statements...
ENDFOR

FOREACH array_expression AS key => value
    statements...
ENDFOR

The first form loops over the array given by array_expression. On each loop, the value of the current element is assigned to value and the internal array pointer is advanced by one (so on the next loop, you'll be looking at the next element).
The second form does the same thing, except that the current element's key will be assigned to the variable key on each loop. This form works only on associative arrays and objects.