_Load( ) returns 0 if the routine is successful. If the routine fails, it returns a negative integer whose absolute value is a Visual FoxPro error number. You can use _Load( ) to retrieve the contents of a memo field, but it doesn't retrieve characters in the field after the first 65,000 bytes. If loc specifies a one-dimensional array, Visual FoxPro returns the value of the first element of the array.

_Load( ) doesn't work with objects. If loc specifies an object reference, _Load( ) returns 0 without filling the val Value structure. Use _Evaluate( ) to obtain an object reference.

If the setting of the Locator field l_offset is – 1, Visual FoxPro returns a logical value structure that indicates whether the current record in the specified work area is deleted:

• ev_length = .T. = DELETED( )

• ev_length = .F. = NOT DELETED( )

  Note
  _Load() creates a handle only when the memory variable your program is loading is a character string (ev_type = 'C'). All other data types store their values in the Value structure itself. Your program must free the handles created with _Load().

For more information on how to create an API library and integrate it with Visual FoxPro, see Accessing the Visual FoxPro API.

The following example converts to uppercase a string argument passed by reference.

Visual FoxPro Code

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SET LIBRARY TO LOAD x = "abc" = XUPPER(@x) ? x

C Code

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#include <pro_ext.h> void FAR Upper(ParamBlk FAR *parm) { char FAR *pString; Value val; int i; // // _Load() and _Store are the functions of interest for pass-by-reference. // _Load(&parm->p[0].loc, &val); // // FoxPro doesn't check the type of pass-by-reference arguments, so we do. // if (val.ev_type != 'C') { _Error(9); // "Data type mismatch" } pString = _HandToPtr(val.ev_handle); for (i = 0; i < val.ev_length; i++) { if ('a' <= *pString && *pString <= 'z') { *pString += ('A' - 'a'); } pString++; } _Store(&parm->p[0].loc, &val); // // We need to free the handle that we created with _LOAD() // _FreeHand(val.ev_handle); } FoxInfo myFoxInfo[] = { {"XUPPER", (FPFI) Upper, 1, "R"}, }; FoxTable _FoxTable = { (FoxTable FAR *) 0, sizeof(myFoxInfo)/sizeof(FoxInfo), myFoxInfo };

Reference

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