How do I use a string in a struct instead of a char array for reading binary data

Question

I am reading binary data into a struct, which is working just fine. Here is the code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

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

int main()
{
  ifstream fin("T201010A.IDX", ios::in | ios::binary);

  if(!fin) {
    cout << "Cannot open file."  << endl;
    return 1;
  }

  int cnt = 0;
  TaqIdx idx;

  while(fin.read((char *) &idx,sizeof(idx))) {
    if(!fin.good()) {
      cout << "A file error occurred." << endl;
      return 1;
    }

    idx.symbol[10] = '\0';
    cout << "(" << idx.symbol << ", " << idx.tdate << ", " 
         << idx.begrec << ", " << idx.endrec << ") "
         << cnt++ << endl;
  }

  fin.close();

  return 0;
}

The first few lines of output are the following:

(A         , 20100864, 1, 35981) 0
(AA        , 20100864, 35982, 89091) 1
(AAPR      , 20100864, 89092, 89093) 2
(AACC      , 20100864, 89094, 89293) 3
(AADR      , 20100864, 89294, 89301) 4
(AAI       , 20100864, 89302, 99242) 5
(AAME      , 20100864, 99243, 99252) 6
(AAN       , 20100864, 99253, 102275) 7
(AANA      , 20100864, 102276, 102280) 8
(AAON      , 20100864, 102281, 102592) 9

My question is this: is it possible to replace the C-style character array in the structure with a C++ string? If so, can you provide an example of how I would do that. Many thanks!

With a bit of effort. If you know this structure has precise byte-layout, and you know that it won't change, your current approach seems optimal (at least compared to bringing in needless abstractions). — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Apr 7, 2011 at 23:40
Programming decision making chart comes to mind: "is it working? => don't f*** with it" :-) — pajton
– pajton, Commented Apr 7, 2011 at 23:45
@Tomalak and @pajton, very nice points. The extra effort may not be worth my time. Thanks. — TJB
– TJB, Commented Apr 7, 2011 at 23:48

Jim Blackler · Accepted Answer · 2011-04-07 23:44:51Z

1

The code appears to be designed to read data serialized with a particular binary format into the TaqIdx format. You could certainly modify the reader to supply the data in a different format (including std::strings) , but you'd either have to rewrite the reader or convert after it had been loaded. Alternatively you could use an entirely different format for the data but that might not be compatible with the files you have.

answered Apr 7, 2011 at 23:44

Jim Blackler

23.3k12 gold badges90 silver badges101 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

octal9 · Accepted Answer · 2011-04-07 23:58:02Z

0

I can't "comment everywhere" yet, so I apologize for this being kind of out of standard protocol around these parts. Why doesn't this break?

idx.symbol[10] = '\0';

The length of symbol is 10, won't having __attribute__((packed)) in there put a null byte into the first byte of tdate?

answered Apr 7, 2011 at 23:58

octal9

3681 silver badge10 bronze badges

2 Comments

TJB Over a year ago

actually you are quite right. I should have noticed this by looking at my output. The second column (dates) are not right. This gets at why I am wanting to use strings instead of char arrays. How do I use cout with a non null-terminated char array? Thanks for the catch.

Lightness Races in Orbit Over a year ago

@TJB: std::cout << std::string(ref_to_array, size_of_array); :)

Collectives™ on Stack Overflow

How do I use a string in a struct instead of a char array for reading binary data

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related