# Pointer writing (Scilab gateway)

How to write pointer in a gateway.
Create from existing data.

## Calling Sequence

Input argument profile:

    SciErr createPointer(void* _pvCtx, int _iVar, void* _pvPtr)

Named variable profile:

    SciErr createNamedPointer(void* _pvCtx, const char* _pstName, void** _pvPtr)

## Arguments

_pvCtx

  Scilab environment pointer, pass in "pvApiCtx" provided by api_scilab.h

_iVar

  Position in the Scilab memory where you want to put the variable

_pstName

  Name of the variable for "named" functions.

_pvPtr

  Address of pointer.

SciErr

  Error structure where is stored errors messages history and first error number.

Write directly in Scilab memory.

## Calling Sequence

    SciErr allocPointer(void* _pvCtx, int _iVar, void** _pvPtr)

## Arguments

_pvCtx

  Scilab environment pointer, pass in "pvApiCtx" provided by api_scilab.h.

_piAddress

  Address of the Scilab variable.

_pvPtr

  Return address of pointer.

SciErr

  Error structure where is stored errors messages history and first error number.

## Description

This help describes how pointer can be handled through the Scilab API.

Two types of functions can be used to write in the memory of Scilab.

## Gateway Source

    #include "api_scilab.h"
    int read_pointer(char *fname,unsigned long fname_len)
    {
    	SciErr sciErr;

    	CheckInputArgument(pvApiCtx, 0, 1);
        CheckOutputArgument(pvApiCtx, 1, 1);

    	if(nbInputArgument(pvApiCtx) == 0)
    	{//create mode
    		double* pdblData    = (double*)malloc(sizeof(double) * 2 * 2);
    		pdblData[0]			= 1;
    		pdblData[1]			= 3;
    		pdblData[2]			= 2;
    		pdblData[3]			= 4;
    		sciErr = createPointer(pvApiCtx, nbInputArgument(pvApiCtx) + 1, (void*)pdblData);
    	}
    	else if(nbInputArgument(pvApiCtx) == 1)
    	{//read mode
    		int iType			= 0;
    		int* piAddr			= NULL;
    		void* pvPtr			= NULL;
    		double* pdblData	= NULL;
    		sciErr = getVarAddressFromPosition(pvApiCtx, 1, &piAddr);
    		if(sciErr.iErr)
    		{
    			printError(&sciErr, 0);
    			return 0;
    		}
    		sciErr = getPointer(pvApiCtx, piAddr, &pvPtr);
    		if(sciErr.iErr)
    		{
    			printError(&sciErr, 0);
    			return 0;
    		}
    		pdblData = (double*)pvPtr;
    		sciErr = createMatrixOfDouble(pvApiCtx, nbInputArgument(pvApiCtx) + 1, 2, 2, pdblData);
    	}
    	else
    	{
    		return 0;
    	}
    	if(sciErr.iErr)
    	{
    		printError(&sciErr, 0);
    		return 0;
    	}
    	AssignOutputVariable(pvApiCtx, 1) = nbInputArgument(pvApiCtx) + 1;
    	return 0;
    }

## Scilab test script

    b_ref = [1,2;3,4];
    a = read_pointer();
    b = read_pointer(a);
    if or(b <> b_ref) then error("failed"), end