Recursively build cell array in MEX? c/c++

Hi, before I even attempt to do this, I wanted to ask if anyone else (including Mathworks staff) has tried to recursively build a cell array? I have to deal with a library (hiredis) that may return nested results in a reply struct. I have to examine the reply type, and if it is a certain type, then I have to traverse all the child replies and examine each of them, etc.

Hiredis sets an arbitrary max nesting level, which I am also going to enforce. I set it to 7, which matches hiredis.

My mind is boggling a bit at what might be involved with recursively adding to the cell array which holds all the results. This is the last major task in writing my redis wrapper and I wish I could just ignore this but there are many redis commands which return replies of a type called "Multi Bulk" which can be arbitrarily nested.

I thought it would be better to ask for help in advance instead of posting a bunch of garbage asking "why I get error".

thx George

Answer 1

[James Tursa]

Generally, you can pretty much build and/or examine "nested" cell or struct mxArray variables in the mex environment using the mxSetCell, mxGetCell, mxSetField, mxGetField etc API functions recursively. If you could provide a short descriptive sample (i.e., pseudo-code) of what you are trying to do we can probably advise how to go about it in C/C++.

[George Coles]

Here is some preliminary code. I am terrible with C, hardly ever do MEX, and am new to Redis, so I am a triple threat.

Edit - here is some code that works to some extent. I am still shaky on memory management and the most elegant way to get data into plhs....

void appendCellArray( mxArray** retVal, int retValRecurseLevel,int recurseMax, redisReply* reply ){

    int numChildren;
    int elementi;
    int replyType;
    mwSize dims[2];

    if (retValRecurseLevel >= recurseMax){
        return;
    }
    replyType = reply->type;
    switch( replyType ){
        case REDIS_REPLY_STRING:
        {
            int index;
            unsigned char* output_array_pointer;
            int numReplyrows = reply->len;

            *retVal = mxCreateNumericMatrix(reply->len, 1, mxUINT8_CLASS, mxREAL);

            output_array_pointer = (unsigned char *)mxGetData(*retVal);
            for ( index = 0; index < numReplyrows; index++ ) {
                output_array_pointer[index] = reply->str[index];
            }
        }
            break;
        case REDIS_REPLY_ARRAY:
            //cell array to hold results            
            numChildren = reply->elements;
            dims[0] = numChildren;
            dims[1] = 1;

            *retVal = mxCreateCellArray( 2, &dims[0] );

            for( elementi = 0; elementi < numChildren; elementi++ ){
                mxArray* childArray;
        redisReply* subreply;
        
        subreply = reply->element[elementi];
                appendCellArray( &childArray, retValRecurseLevel,recurseMax, subreply );
                mxSetCell( *retVal, elementi, childArray );
            }
            break;
        case REDIS_REPLY_INTEGER:
        {
            *retVal = mxCreateDoubleScalar( reply->integer );
        }
            break;
        case REDIS_REPLY_NIL:
        {
            const mwSize emptyDims[2] = {0,0};
            *retVal = mxCreateNumericArray( 2,emptyDims,mxUINT8_CLASS,mxREAL );
        }

            break;
        case REDIS_REPLY_STATUS:
            *retVal = mxCreateString( reply->str );
            break;
        case REDIS_REPLY_ERROR:
            *retVal = mxCreateString( reply->str );
            break;
        default:
            freeReplyObject(reply);
            mexErrMsgTxt("we do not know how to deal with this reply type");
    }
}

[George Coles]

no comment on whether I am doing it right?

[Jan]

In general the code looks ok. There are two strong testers on your computer: 1. let the compiler parse the input, 2. let the code run and test the results with your expectations.

Btw., this is not C-code, but C++, because the later allows to declare variables inside the code. But as long as the compiler accept this, this is a cosmethical aspect only.