Im trying to learn D, lovely language for a C++ lover. I have a file Im trying to parse, but I need to read the contents as binary data. I also need help understanding how read() works. I'd like to read the first four bytes which identify the file header, I need it to show as a sequence of bytes, how can i output the first 4 bytes to show like 0xFFCF?

With my code, im getting the integer values, If i use cast(byte[]) on read and writefln("Reading header info: 0x%x", bytesRead[0]);

Ill only get the first byte 0xCF.


import std.stdio;
import std.file;
import std.array;

struct xsdhead{
    int head1;
    int head2;
    int numTables;
};

immutable int headerInfo1 = 0xFFCF;
immutable int headerInfo2 = 0x0002;

int main(string [] args){
    writeln("start");
    if(args[1] == null){
        writeln("pass a file");
        return 0;
    }
    auto file = args[1];
    writeln("Working on ", file);

    auto bytesRead =  cast(byte[]) read(file, 4);
    writefln("Reading header info: %s", bytesRead);
    writefln("Address of caret is: 0x%X", &bytesRead);

    return 0;
}

On Wednesday, 29 May 2013 at 22:03:24 UTC, baws wrote:
> Im trying to learn D, lovely language for a C++ lover. I have a file Im trying to parse, but I need to read the contents as binary data. I also need help understanding how read() works. I'd like to read the first four bytes which identify the file header, I need it to show as a sequence of bytes, how can i output the first 4 bytes to show like 0xFFCF?
>
> With my code, im getting the integer values, If i use cast(byte[]) on read and writefln("Reading header info: 0x%x", bytesRead[0]);
>
> Ill only get the first byte 0xCF.
>
>
> import std.stdio;
> import std.file;
> import std.array;
>
> struct xsdhead{
>     int head1;
>     int head2;
>     int numTables;
> };
>
> immutable int headerInfo1 = 0xFFCF;
> immutable int headerInfo2 = 0x0002;
>
> int main(string [] args){
>     writeln("start");
>     if(args[1] == null){
>         writeln("pass a file");
>         return 0;
>     }
>     auto file = args[1];
>     writeln("Working on ", file);
>
>     auto bytesRead =  cast(byte[]) read(file, 4);
>     writefln("Reading header info: %s", bytesRead);
>     writefln("Address of caret is: 0x%X", &bytesRead);
>
>     return 0;
> }

Oh clap guys, sorry for wasting time, I just noticed the std.stdio.File library! Ill come back to this later!

On Wednesday, 29 May 2013 at 22:03:24 UTC, baws wrote:
> With my code, im getting the integer values, If i use cast(byte[]) on read and writefln("Reading header info: 0x%x", bytesRead[0]);

You're reading the file correctly, just not printing it all out in hex.

>     writefln("Reading header info: %s", bytesRead);

this line should be printing the right data, just in decimal notation instead of hex. If you do the %x with one byte at a time you'll probably get the output you want:

        byte[] a = [10, 16, 32, 123];
        writef("0x");
        foreach(b; a)
            writef("%x", b);
        writef("\n");

On 05/29/2013 03:23 PM, Adam D. Ruppe wrote:

>          byte[] a = [10, 16, 32, 123];
>          writef("0x");
>          foreach(b; a)
>              writef("%x", b);
>          writef("\n");

There is also the nested array formatting. Pretty cool but dyslecix! :)

    writefln("0x%(%x%)", a);

Ali

Ali Çehreli:

>     writefln("0x%(%x%)", a);

But usually I prefer to show all the zero nibbles:

void main() {
    import std.stdio;
    ubyte[] a = [10, 16, 32, 123];
    writefln("0x%(%02x%)", a); // Output: 0xa10207b
    static assert(is(typeof(a[0]) == ubyte), "Only ubyte[]");
    writefln("0x%(%x%)", a);   // Output: 0x0a10207b
}

Bye,
bearophile

> void main() {
>     import std.stdio;
>     ubyte[] a = [10, 16, 32, 123];
>     writefln("0x%(%02x%)", a); // Output: 0xa10207b
>     static assert(is(typeof(a[0]) == ubyte), "Only ubyte[]");
>     writefln("0x%(%x%)", a);   // Output: 0x0a10207b
> }

I have pasted the outputs inverted, sorry.

Bye,
bearophile

On 05/29/2013 04:11 PM, bearophile wrote:

> Ali Çehreli:
>
>>     writefln("0x%(%x%)", a);
>
> But usually I prefer to show all the zero nibbles:

>      writefln("0x%(%02x%)", a); // Output: 0xa10207b

And only then the output would make sense. Thanks. :)

Ali

On Wednesday, 29 May 2013 at 22:03:24 UTC, baws wrote:
> Im trying to learn D, lovely language for a C++ lover. I have a file Im trying to parse, but I need to read the contents as binary data. I also need help understanding how read() works. I'd like to read the first four bytes which identify the file header, I need it to show as a sequence of bytes, how can i output the first 4 bytes to show like 0xFFCF?
>
> With my code, im getting the integer values, If i use cast(byte[]) on read and writefln("Reading header info: 0x%x", bytesRead[0]);
>
> Ill only get the first byte 0xCF.
>
>
> import std.stdio;
> import std.file;
> import std.array;
>
> struct xsdhead{
>     int head1;
>     int head2;
>     int numTables;
> };
>
> immutable int headerInfo1 = 0xFFCF;
> immutable int headerInfo2 = 0x0002;
>
> int main(string [] args){
>     writeln("start");
>     if(args[1] == null){
>         writeln("pass a file");
>         return 0;
>     }
>     auto file = args[1];
>     writeln("Working on ", file);
>
>     auto bytesRead =  cast(byte[]) read(file, 4);
>     writefln("Reading header info: %s", bytesRead);
>     writefln("Address of caret is: 0x%X", &bytesRead);
>
>     return 0;
> }

Erhm, why isnt this compiling guys? all i did was add your suggestions... :/

import std.stdio;
import std.file;
import std.array;

struct xsdhead{
    int head1;
    int head2;
    int numTables;
};

immutable int headerInfo1 = 0xFFCF;
immutable int headerInfo2 = 0x0002;

int main(string [] args){
    writeln("start");
    if(!args[1]){
        writeln("pass a file");
        return 0;
    }
    auto file = args[1];
    writeln("Working on: ", file);

    auto bytesRead =  cast(byte[])read(file, 4);
    writefln("Reading header info: 0x%(%02x%)", bytesRead);

    return 0;
}

On 05/29/2013 09:00 PM, baws wrote:

> Erhm, why isnt this compiling guys? all i did was add your
> suggestions... :/

Your code compiles here with dmd 2.062 and v2.063-devel-f6d55a9-dirty. What is the compiler error in your case?

The program has a run time error though: args[1] is an invalid access when args has only one element. Also, you are making an incorrect assumption: Unlike C, the last element of args is not null; such an element simply does not exist. You need a check like this:

    if (args.length != 2) {
        // ...
    }

Ali