You can specify any expression that can be evaluated by the Visual FoxPro EVALUATE( ) function. After the expression is evaluated, control usually returns to the C statement immediately following the call to _Evaluate( ). Exceptions include evaluating a Visual FoxPro expression that carries out a Visual FoxPro CANCEL or QUIT command.

_Evaluate( ) returns the Visual FoxPro internal error number for any errors that occur during evaluation of the Visual FoxPro expression, or returns 0 if no errors occur. The contents of res are valid only when _Evaluate( ) returns a value of 0.

Note
Do not call _Evaluate() from an event handler.

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 has the same functionality as the Visual FoxPro EVALUATE( ) function.

Visual FoxPro Code

	Copy Code
SET LIBRARY TO EVALUATE ? XEVAL("2 + 3") ? XEVAL("'a' + 'b'") ? XEVAL("SIN(PI()/2))")

C Code

Copy Code

#include <pro_ext.h> FAR EvaluateEx(ParamBlk FAR *parm) { char FAR *expr; Value result; // Null terminate character string if (!_SetHandSize(parm->p[0].val.ev_handle, parm->p[0].val.ev_length + 1)) { _Error(182); // "Insufficient memory" } _HLock(parm->p[0].val.ev_handle); expr = (char FAR *) _HandToPtr(parm->p[0].val.ev_handle); expr[parm->p[0].val.ev_length] = '\0'; _Evaluate(&result, expr); _RetVal(&result); _HUnLock(parm->p[0].val.ev_handle); } FoxInfo myFoxInfo[] = { {"XEVAL", (FPFI) EvaluateEx, 1, "C"}, }; FoxTable _FoxTable = { (FoxTable FAR *) 0, sizeof(myFoxInfo)/sizeof(FoxInfo), myFoxInfo };

Reference

Other Resources