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POUnderstanding binary conversions
 

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  1. POUnderstanding binary conversions
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    <p>I'm writing a resource file which I want to insert a bunch of data from various common files such as .JPG, .BMP (for example) and I want it to be in binary. I'm going to code something to retrieve these data later on organized by index, and this is what I got so far:</p> <pre><code>float randomValue = 23.14f; ofstream fileWriter; fileWriter.open("myFile.dat", ios::binary); fileWriter.write((char*)&amp;randomValue, sizeof(randomValue)); fileWriter.close(); //With this my .dat file, when opened in notepad has "B!¹A" in it float retrieveValue = 0.0f; ifstream fileReader; fileReader.open("myFile.dat", ios::binary); fileReader.read((char*)&amp;retrieveValue, sizeof(retrieveValue)); fileReader.close(); cout &lt;&lt; retrieveValue &lt;&lt; endl; //This gives me exactly the 23.14 I wanted, perfect! </code></pre> <p>While this works nicely, I'd like to understand what exactly is happening there. I'm converting the address of <em>randomValue</em> to char*, and writing the values in this address to the file?</p> <p>I'm curious also because I need to do this for an array, and I can't do this:</p> <pre><code>int* myArray = new int[10]; //fill myArray values with random stuff fileWriter.open("myFile.dat", ios::binary); fileWriter.write((char*)&amp;myArray, sizeof(myArray)); fileWriter.close(); </code></pre> <p>From what I understand, this would just write the first address' value in the file, not all the array. So, for testing, I'm trying to simply convert a variable to a char* which I would write to a file, and convert back to the variable to see if I'm retrieving the values correctly, so I'm with this:</p> <pre><code>int* intArray = new int[10]; for(int i = 0; i &lt; 10; i++) { cout &lt;&lt; &amp;intArray[i]; //the address of each number in my array cout &lt;&lt; intArray[i]; //it's value cout &lt;&lt; reinterpret_cast&lt;char*&gt;(&amp;intArray[i]); //the char* value of each one } </code></pre> <p>But for some reason I don't know, my computer "beeps" when I run this code. During the array, I'm also saving these to a char* and trying to convert back to int, but I'm not getting the results expected, I'm getting some really long values. Something like:</p> <pre><code>float randomValue = 23.14f; char* charValue = reinterpret_cast&lt;char*&gt;(&amp;randomValue); //charValue contains "B!¹A" plus a bunch of other (un-initiallized values?) characters, so I'm guessing the value is correct //Now I'm here </code></pre> <p>I want to convert charValue back to randomValue, how can I do it?</p> <p><strong>edit</strong>: There's valuable information in the answers below, but they don't solve my (original) problem. I was testing these type of conversions because I'm doing a code that I will pick a bunch of resource files such as BMP, JPG, MP3, and save them in a single .DAT file organized by some criteria I still haven't fully figured out.</p> <p>Later, I am going to use this resource file to read from and load these contents into a program (game) I'm coding.</p> <p>The criteria I am still thinking but I was wondering if it's possible to do something like this:</p> <pre><code>//In my ResourceFile.DAT [4 bytes = objectID][3 bytes = objectType (WAV, MP3, JPG, BMP, etc)][4 bytes = objectLength][objectLength bytes = actual objectData] //repeating this until end of file </code></pre> <p>And then in the code that reads the resource file, I want to do something like this (untested):</p> <pre><code>ifstream fileReader; fileReader.open("myFile.DAT", ios::binary); //file check stuff while(!fileReader.eof()) { //Here I'll load int objectID = 0; fileReader((char*)&amp;objectID, 4); //read 4 bytes to fill objectID char objectType[3]; fileReader(&amp;objectType, 3); //read the type so I know which parser use int objectLength = 0; fileReader((char*)&amp;objectLength, 4); //get the length of the object data char* objectData = new char[objectLength]; fileReader(objectData, objectLength); //fill objectData with the data //Here I'll use a parser to fill classes depending on the type etc, and move on to the next obj } </code></pre> <p>Currently my code is working with the original files (BMP, WAV, etc) and filling them into classes, and I want to know how I can save the data from these files into a binary data file. For example, my class that manages BMP data has this:</p> <pre><code>class FileBMP { public: int imageWidth; int imageHeight; int* imageData; } </code></pre> <p>When I load it, I call:</p> <pre><code>void FileBMP::Load(int iwidth, int iheight) { int imageTotalSize = iwidth * iheight * 4; imageData = new int[imageTotalSize]; //This will give me 4 times the amount of pixels in the image int cPixel = 0; while(cPixel &lt; imageTotalSize) { imageData[cPixel] = 0; //R value imageData[cPixel + 1] = 0; //G value imageData[cPixel + 2] = 0; //B value imageData[cPixel + 3] = 0; //A value cPixel += 4; } } </code></pre> <p>So I have this single dimension array containing values in the format of [RGBA] per pixel, which I am using later on for drawing on screen. I want to be able to save just this array in the binary data format that I am planning that I stated above, and then read it and fill this array.</p> <p>I think it's asking too much for a code like this, so I'd like to understand what I need to know to save these values into a binary file and then read back to fill it.</p> <p>Sorry for the long post!</p> <p><strong>edit2:</strong> I solved my problem by making the first edit... thanks for the valuable info, I also got to know what I wanted to!</p>
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