iOS Can I read a binary data file into struct?

[mikezang]

I have a binary data file in format as below:

struct {
    int32 day; // days since 1900-01-01
    int32 open;
    int32 high;
    int32 low;
    int32 close;
    double64 volume;
} StockData;

I know I can read this file by code as below:

StockData stockData; 
NSArray StockList* = [[NSArray alloc] initWithObjects:stockData];
NSData *data = [NSData dataWithContentsOfFile:myFile];
// How to copy data to stockData of stockList

My question is how can I copy data into stockData, so that I can use code as below to access them?

int day = [StockList objectAtIndex:0].day;
int open = [StockList objectAtIndex:0].open;
int high = [StockList objectAtIndex:0].high;
int low = [StockList objectAtIndex:0].low;
int close = [stockData objectAtIndex:0].close;
float volume = [StockList objectAtIndex:0].volume;

 

[robbieduncan]

I don't see what the difficulty is. NSData will give you a pointer to the bytes. Once you have that it's basic C pointer arithmetic an dereferencing.

 

[mikezang]

I don't see what the difficulty is. NSData will give you a pointer to the bytes. Once you have that it's basic C pointer arithmetic an dereferencing.

Well, I will try it.

 

[mikezang]

I used code as below to do this task, but I couldn't get correct result, can you help me?

struct Stock {
    int day;   // data in 4 bytes
    int open; // data in 4 bytes
    int high;  // data in 4 bytes
    int low;   // data in 4 bytes
    int close; // data in 4 bytes
    double volume;// data in 8bytes
};

-(IBAction) convert:(id)sender {
    NSError *error = nil;
    NSBundle *bundle = [NSBundle mainBundle];
    NSData *data = [NSData dataWithContentsOfFile:[bundle pathForResource:@"9984" ofType:@""] options:0 error:&error];
	
    if (error) {
        NSLog(@"%@", error);
    }
    else {
        struct Stock *stock = (struct Stock*)[data bytes];
        void *last = stock + [data length];
			  
        while ((void*)stock < last) {
            NSLog(@"%d, %d, %d, %d, %d, %.3f", stock->day, stock->open, stock->high, stock->low, stock->close, stock->volume);
			
            stock += sizeof(struct Stock);
        }
    }
}

 

[PhoneyDeveloper]

It is a simple and well known fact that you don't read/write structs from/to files. In order to implement this simple process you need to understand (1) struct padding and (2) endianness. Read/write the data member by member in order to avoid struct padding problems. Learn about endian issues to get that correct.

 

[mikezang]

It is a simple and well known fact that you don't read/write structs from/to files. In order to implement this simple process you need to understand (1) struct padding and (2) endianness. Read/write the data member by member in order to avoid struct padding problems. Learn about endian issues to get that correct.

Can you show me detail way? I need to solve my problems, if I study from zero, I don't think I can do anything

 

[mikezang]

Well, I got what I need as below:

struct Stock {
    int day;   // data in 4 bytes
    int open; // data in 4 bytes
    int high;  // data in 4 bytes
    int low;   // data in 4 bytes
    int close; // data in 4 bytes
    double volume;// data in 8bytes
};

-(IBAction) convert:(id)sender {
    NSError *error = nil;
    NSBundle *bundle = [NSBundle mainBundle];
    NSData *data = [NSData dataWithContentsOfFile:[bundle pathForResource:@"9984" ofType:@""] options:0 error:&error];
	
    if (error) {
        NSLog(@"%@", error);
    }
    else {
        struct Stock *stock = (struct Stock*)[data bytes];
			  
        while (stock->day > 0) {
            NSLog(@"%d, %d, %d, %d, %d, %.3f", stock->day, stock->open, stock->high, stock->low, stock->close, stock->volume);
			
            stock++;
        }
    }
}

 

[PhoneyDeveloper]

The code you show is very brittle. It might work with some structs and some compilers and some hardware but it's not a general solution.

http://www.google.com/search?hl=en&...hts=&as_occt=any&cr=&as_nlo=&as_nhi=&safe=off

 

[robbieduncan]

It really isn't what I intended. I had assumed you'd step down the bytes reading an int or float off at a time and converting as required. But the above is correct: binary dumping structs to/from a file is really not a good idea.

 

[mikezang]

It really isn't what I intended. I had assumed you'd step down the bytes reading an int or float off at a time and converting as required. But the above is correct: binary dumping structs to/from a file is really not a good idea.

You are right, I am doing to convert that file to SQLite3, I just use that file which made by other people.