Description
Binary File I/O
Overview
In this assignment, you are going to load a series of files containing data and then searching the loaded data for specific criteria (This sounds oddly familiar…). The files that you load will contain information about various hero characters, some of their attributes (i.e. strength, hit-points, etc.) as well as any items they may be carrying. The data that you load will also be in a binary format, which needs to be handled differently than text-based files.
Reading binary data
Reading data in binary is all about copying bytes (1 byte := 2 nibbles := 8 bits) from a location in a file to a location in memory. When reading data you will always use the read() function, and when writing data you will always use the write() function. For this assignment, you will only need to read() data.
Strings are always an exceptional case. In the case of strings, you should read them in a 4 or 5 step process:
- Read the length of the string from the file. Unless you are dealing with fixed-length strings (in which case you know the length of the string from somewhere else), it will be there, promise. (If someone didn’t write this data out to a file, shame on them, they screwed up.)
- Dynamically allocate an array equal to the size of the string, plus 1 for the null terminator. If the length already includes the null terminator, do not add one to the count here — you’d be accounting for it twice, which is bad.
- Read the string into your newly created buffer.
- (OPTIONAL) Store your dynamic char * in something like a std::string, which manages its own internal memory. Then you don’t have to worry about it anymore.
- Delete the dynamically allocated array. If you did step 4, this should be immediately after you store it in the std::string (so you don’t forget to delete it later). If you are planning to use this variable later, be sure to delete it later on down the line.
Refer back to the Powerpoint slides about Binary File I/O for information on how to read and write binary files.
File format
The structure of the files is as follows:
| 4 bytes | A count of how many ships are in the file |
| “Count” number of ships follow the first 4 bytes. Each ship has the following format: | |
| 4 bytes | The length of the name, including the null terminator |
| “Length” bytes | The string data for the name, including the null terminator |
| 4 bytes | The length of the ship’s class, including the null terminator |
| “Length” bytes | The string data for the class, including the null terminator |
| 2 bytes | The ship’s length, in meters |
| 4 bytes | The ship’s shield capacity, in terajoules |
| 4 bytes | The warp speed of the ship |
| 4 bytes | A count of the number of weapons equipped on the ship |
| “Count” number of weapons follow the previous 4 bytes. Each Item is as follows: | |
| 4 bytes | The length of the weapon’s name, including the null terminator |
| “Length” bytes | The string data for the name of the item, including the null terminator |
| 4 bytes | An integer for power rating of the weapon (on some fictional scale—higher is better) |
| 4 bytes | A float for the power consumption of the weapon |
Searches
After you’ve loaded the data, you will perform a few operations on the stored data:
- Print all the ships
- Print the starship with the most powerful weapon
- Print the most powerful ship (highest combined power rating of all weapons)
- Print the weakest ship (out of ships that actually have weapons)
- Print the unarmed ships
Sample outputs
Left: First 2 ships from enemyships.shp — Right: Unarmed friendly vessels
