Question

I am trying to build a messageQueue based around this messageStruct

struct MessageStruct{
    public: std::string msg;     // what is the msg
    public: int prior;           // how important is this msg
};

That lies in a MessageQueue that is needed to act like a vector/priorityQueue (self made version that is working fine), but I put a bunch of stuff on it, like so.

int size = 20;
// constructor takes number of entries to start with
MessageQueue * queue = new MessageQueue(size);
// used as a transport mechanism
MessageStruct * msg = new MessageStruct();
msg->prior = 0;
msg->msg = "queue exists";
queue->getMsg(msg);
// increasing size does not cause memory issue,
//  use for example of dynamic size.
... other stuff is happening
size *= 2;
for (int ii = 0; ii < size; ii++){
    msg->prior = 0;
    msg->msg = "creating thing " + ii;
    // puts this message in the queue,
    //  and increases queue size if needed
    queue->getMsg(msg);
}
... // other stuff is happening
msg->prior = 10;
msg->msg = "program terminated correctly";
queue->queueDump();
delete msg;
msg = 0;
delete queue;
queue = 0;

This code gets no errors, and all memory is being released without issue, though the output of this looks like this (I generate the output in xml for sanity):

<message> 
    <index>0</index>
    <msg>program terminated correctly</msg>
    <priority>10</priority>
</message>
<message> 
    <index>1</index>
    <msg>init(). queue exists</msg>
    <priority>0</priority>
</message>
<message> 
    <index>2</index>
    <msg>reating thing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>3</index>
    <msg>eating thing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>4</index>
    <msg>ating thing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>5</index>
    <msg>ting thing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>6</index>
    <msg>ing thing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>7</index>
    <msg>ng thing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>8</index>
    <msg>g thing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>9</index>
    <msg> thing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>10</index>
    <msg>thing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>11</index>
    <msg>hing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>12</index>
    <msg>ing </msg>
    <priority>0</priority>
</message>
<message> 
    <index>13</index>
    <msg>ng </msg>
    <priority>0</priority>
</message>
<message> 
    <index>14</index>
    <msg>g </msg>
    <priority>0</priority>
</message>
<message> 
    <index>15</index>
    <msg> </msg>
    <priority>0</priority>
</message>

It looks like the strings are being generated and placed, but why are leading characters being removed?

Answer 1

needed to introduce a method to the code that converted an int to a string

//----------
// attempts to convert a int to a string
//----------
string toString(int value) {   // may need to specify std::
    string result = "";
    bool negative = false;
    if ( value < 0 ) {
        negative = true;
        value *= (-1);
    }
    do {
        string tmpstr = "0";
        tmpstr[0] += value%10;
        result = tmpstr + result;
        value /= 10;
    } while ( value != 0);
    if ( negative ) {
        result = "-" + result;
    }
    return result;
}

then modify the line

msg->msg = "creating thing " + ii;

to be

msg->msg = "creating thing " + toString(ii);

this can be costly to do in repetition, but the only other option is likely to call a string builder that doesn’t really save anything