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Reading binary file data into List of Structs


Reading binary file data into List of Structs

By : user2187030
Date : November 26 2020, 04:01 AM
wish helps you When you are serializing data as binary, your deserialization code must follow serialization code exactly; otherwise your deserializer starts reading junk from adjacent positions, eventually causing an exception or silently populating your structures with wrong data.
This pair of calls is mismatched:
code :
writerToFile.Write(book.BookID);
....
CurrentRecord.BookID = readerFromFile.ReadInt16();
CurrentRecord.BookID = readerFromFile.ReadInt32();


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sequentially reading a structs from binary file in C++

sequentially reading a structs from binary file in C++


By : Colin Chase
Date : March 29 2020, 07:55 AM
wish help you to fix your issue You can skip sequential read only if the file contains structures of the same size, or uses some index table.
For the case of structures of same size:
code :
void ReadStudent(istream &src, Student &dst)
{
    src.read(&dst, sizeof(dst));
}

void GoToStudentIndex(istream &src, size_t idx)
{
   src.seekg(idx * sizeof(Student), is.beg);
 }
void WriteStudent(ostream &dst, const Student &src)
{
    dst.write(&src, sizeof(src));
}
Reading binary file to a list of structs, but deepcopy overwrites first structs

Reading binary file to a list of structs, but deepcopy overwrites first structs


By : Kyle
Date : March 29 2020, 07:55 AM
hope this fix your issue I am reading a binary file into a list of class instances. I have a loop that reads data from the file into an instance. When the instance is filled, I append the instance to a list and start reading again. , You have two problems here:
code :
self.rect = Rect()  # note parentheses
g.rect.L = unpack('i',f.read(4))[0]
g = groundtruthfile()
for _ in range(length[0]):
for i in range(1,length[0]+1):
Writing and reading structs from binary file that contain other structs (C)

Writing and reading structs from binary file that contain other structs (C)


By : EL Mehdi Fatih
Date : March 29 2020, 07:55 AM
may help you . The problem is that you're writing the pointer to the file, that should end in something like this
21 chars -> coming from the char array "name" from struct shop
code :
typedef struct shop
{
    char name[21];
    int numOfItems;
    ITEMS arr;
} SHOP;
Reading a certain position in a binary file using structs with pointers

Reading a certain position in a binary file using structs with pointers


By : RavynX
Date : March 29 2020, 07:55 AM
I wish did fix the issue. You cannot call fseek(p, pos* sizeof(user), SEEK_SET); to skip to pos user in your file. sizeof(user) returns size in bytes of user struct but you have pointer following in this struct, which points to array filled by your following objects. If you want to skip to pos user you should have information how many following objects are in each user. You don't have this information so you can read your file user one by one to reach pos user.
code :
// pseudocode 
get_user_info (int pos) {
   while (pos--) {
      skip 6 bytes // nick
      read 4 bytes n_following;
      skip n_following * sizeof(following) bytes
   }
   // here you can read data of pos user
}
Randomly reading structs from a binary file

Randomly reading structs from a binary file


By : Hắc Công Tử
Date : March 29 2020, 07:55 AM
it helps some times You can't, with the structure you've got - the records could be any size. In order to seek to an arbitrary record, you either need to have a fixed size of record (which would mean having some limit on the size of your name and category strings, and then padding the records with empty space if they're smaller than that limit) or you need to build up a separate index, which would basically be fixed-sized records saying "record X starts at position Y".
Note that the latter approach makes editing a record tricky, as unless the new version is exactly the same size as the old one, you either need to keep it in place but "waste" some space at the end of the record, or create a new record at the end of the file.
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