• TJB (72/72) Mar 13 2014 I am a bit confused by the alignment of a struct in D. I have
• Justin Whear (4/6) Mar 13 2014 It did change a few versions ago (not sure exactly when). Try adding
• bearophile (10/13) Mar 13 2014 Yes it's a recent change, the align() on outside is the alignment
• TJB (3/16) Mar 14 2014 Thanks! That was it.

"TJB" <broughtj gmail.com> writes:

I am a bit confused by the alignment of a struct in D.  I have 
some C++ code that I am translating into D.

Here is the C++:

#include <fstream>
#include <iostream>
#include <string.h>

struct TradesIdx
{
   char symbol[10];
   int tdate;
   int begrec;
   int endrec;
}__attribute__((packed));

struct TradesBin
{
   int ttim;
   int prc;
   int siz;
   short int g127;
   short int corr;
   char cond[2];
   char ex[1];
}__attribute__((packed));

int main()
{
   std::string 
infile("/Users/tyler/BFE/Measures/data/201212/T201212A.IDX");
   std::ifstream fin(infile.c_str(), std::ios::in | 
std::ios::binary);

   std::cout << "Size of TradesIdx = " << sizeof(TradesIdx) << 
std::endl;
   std::cout << "Size of TradesBin = " << sizeof(TradesBin) << 
std::endl;

   return 0;
}

Which when run gives the values:

Size of TradesIdx = 22
Size of TradesBin = 19

Here is the D code:

import std.stdio : writefln;
import std.stream;

align(1) struct TradesIdx
{
   char[10] symbol;
   int tdate;
   int begrec;
   int endrec;
}

align(1) struct TradesBin
{
   int ttim;
   int prc;
   int siz;
   short g127;
   short corr;
   char[2] cond;
   char[1] ex;
}

void main()
{
   string infile = 
"/Users/tyler/BFE/Measures/data/201212/T201212A.IDX";
   auto fidx = new File(infile, FileMode.In);

   writefln("Size of TradesIdx = %s", TradesIdx.sizeof);
   writefln("Size of TradesBin = %s", TradesBin.sizeof);
}

Which when run gives:

Size of TradesIdx = 24
Size of TradesBin = 19

Why the difference?  What is weird is that the two codes used to 
give the same answers. Has the alignment value of structs changed 
recently?

Justin Whear <justin economicmodeling.com> writes:

On Thu, 13 Mar 2014 23:19:59 +0000, TJB wrote:
 
 Why the difference?  What is weird is that the two codes used to give
 the same answers. Has the alignment value of structs changed recently?

It did change a few versions ago (not sure exactly when).  Try adding 
`align(1):` inside the structs before the members. 

"bearophile" <bearophileHUGS lycos.com> writes:

Justin Whear:

 It did change a few versions ago (not sure exactly when).  Try 
 adding
 `align(1):` inside the structs before the members.

Yes it's a recent change, the align() on outside is the alignment 
of the whole struct, and the align inside is the alignment of the 
single field relative to the start of the struct or the precedent 
field.

align(1) struct Foo {
     align(1) double x;
}

Bye,
bearophile

"TJB" <broughtj gmail.com> writes:

On Friday, 14 March 2014 at 00:07:12 UTC, bearophile wrote:
 Justin Whear:

 It did change a few versions ago (not sure exactly when).  Try 
 adding
 `align(1):` inside the structs before the members.

 Yes it's a recent change, the align() on outside is the 
 alignment of the whole struct, and the align inside is the 
 alignment of the single field relative to the start of the 
 struct or the precedent field.

 align(1) struct Foo {
     align(1) double x;
 }

 Bye,
 bearophile

Thanks!  That was it.

TJB