dev-cpp-users

[Dev-C++] A bit stumped on binary files

[Ewald H. <in...@ho...>]

Hi,

I use the attached code to output a struct to a binary file. Outputting =
character arrays is no problem, but how do I output an integer value in =
bytes and not a string value ? I will be using the Win32 platform, =
32-bit integer, so portability is no issue. Is there an easy way to do =
it that would simply output the required 4 bytes ? My current test =
solution converts a number to a 10 digit string, padded with 0's like =
this : 10 would be 0000000010, but it is clumsy!

Regards
Ewald Horn
Proprietor/Eienaar : Horn Labs
Cell/Sel : 083 519 1615
Website : http://www.hornlabs.co.za
Email/E-pos : in...@ho...


//[code]

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

using namespace std;

struct MyStruct
{
  char name[40];
  char surname[40];
  int age;
}; =20

// global
ofstream myFile("tmp.out",ios::out | ios::binary);

void writeStruct(MyStruct);

int main()
{
  MyStruct data[3] =3D {0};
 =20
  for (int i =3D 0; i < 3; i++)
    writeStruct(data[i]);
 =20
  myFile.close();
 =20
  return 0;
} =20


void writeStruct(MyStruct strc)
{
  for (int i =3D 0; i < sizeof(strc.name); i++)
    myFile.put(strc.name[i]);

  for (int i =3D 0; i < sizeof(strc.surname); i++)
    myFile.put(strc.surname[i]);

// problem area follows   =20
  myFile << strc.age;
} =20
//[end code]

Re: [Dev-C++] A bit stumped on binary files

[Jorge A. <jor...@ep...>]

In fopen you can specify a binary stream with the b modifier in the=20
wanted open type (glibc reference).

Ewald Horn escribi=F3:

> Hi,
> =20
> I use the attached code to output a struct to a binary file.=20
> Outputting character arrays is no problem, but how do I output an=20
> integer value in bytes and not a string value ? I will be using the=20
> Win32 platform, 32-bit integer, so portability is no issue. Is there=20
> an easy way to do it that would simply output the required 4 bytes ?=20
> My current test solution converts a number to a 10 digit string,=20
> padded with 0's like this : 10 would be 0000000010, but it is clumsy!
> =20
> Regards
> Ewald Horn
> Proprietor/Eienaar : Horn Labs
> Cell/Sel : 083 519 1615
> Website : http://www.hornlabs.co.za
> Email/E-pos : in...@ho... <mailto:in...@ho...>
> =20
> //[code]
> =20
> #include <fstream>
> #include <string.h>
> =20
> using namespace std;
> =20
> struct MyStruct
> {
>   char name[40];
>   char surname[40];
>   int age;
> };=20
> =20
> // global
> ofstream myFile("tmp.out",ios::out | ios::binary);
> =20
> void writeStruct(MyStruct);
> int main()
> {
>   MyStruct data[3] =3D {0};
>  =20
>   for (int i =3D 0; i < 3; i++)
>     writeStruct(data[i]);
> =20
>   myFile.close();
> =20
>   return 0;
> }=20
> =20
> void writeStruct(MyStruct strc)
> {
>   for (int i =3D 0; i < sizeof(strc.name); i++)
>     myFile.put(strc.name[i]);
> =20
>   for (int i =3D 0; i < sizeof(strc.surname); i++)
>     myFile.put(strc.surname[i]);
> // problem area follows   =20
>   myFile << strc.age;
> }=20
> //[end code]

Re: [Dev-C++] A bit stumped on binary files

[Ewald H. <in...@ho...>]

>In fopen you can specify a binary stream with the b modifier in the
>wanted open type (glibc reference).


I do open the file as binary, using an IO stream. That's not the problem. I
need to know how to convert an integer value into it's 4 byte equivalent.
For instance 39184 is $00009910 and I would like to write [00,00,99,10] as
hex values to my file. I was just wondering if there was a way to dump an
entire struct to a file and then read it back later.


Regards
Ewald Horn
Proprietor/Eienaar : Horn Labs
Cell/Sel : 083 519 1615
Website : http://www.hornlabs.co.za
Email/E-pos : in...@ho...

Re: [Dev-C++] A bit stumped on binary files

[Daniel K. O. <dan...@ya...>]

Ewald Horn wrote:

>I do open the file as binary, using an IO stream. That's not the problem. I
>need to know how to convert an integer value into it's 4 byte equivalent.
>  
>

No conversion is needed. Actually, your problem is that you ARE 
converting it to a string. The << operator is overloaded to convert the 
integer in a string representation of the value. You should be using the 
.write() method of the stream.

Check this:
http://www.cplusplus.com/ref/iostream/ostream/write.html



>For instance 39184 is $00009910 and I would like to write [00,00,99,10] as
>hex values to my file.
>  
>

In that case you'll need the << operator with the "hex" manipulator.
http://www.cplusplus.com/ref/iostream/ios_base/_dec_hex_oct.html


Daniel K. O.

Re: [Dev-C++] A bit stumped on binary files

[Ewald H. <in...@ho...>]

> No conversion is needed. Actually, your problem is that you ARE
> converting it to a string. The << operator is overloaded to convert the
> integer in a string representation of the value. You should be using the
> .write() method of the stream.
>
> Check this:
> http://www.cplusplus.com/ref/iostream/ostream/write.html

Awesome!

Funny my C++ manual does not mention this write method. Guess it's time for
a new one then.

Thank you for all the answers.

Thank you
Ewald Horn
Proprietor/Eienaar : Horn Labs
Cell/Sel : 083 519 1615
Website : http://www.hornlabs.co.za
Email/E-pos : in...@ho...

Re: [Dev-C++] A bit stumped on binary files

[Per W. <pw...@ia...>]

Just do:

int i = 10;

(char*)i;

and write out sizeof(i) bytes.

/Per W

On Sat, 22 May 2004, Ewald Horn wrote:

> >In fopen you can specify a binary stream with the b modifier in the
> >wanted open type (glibc reference).
>
>
> I do open the file as binary, using an IO stream. That's not the problem. I
> need to know how to convert an integer value into it's 4 byte equivalent.
> For instance 39184 is $00009910 and I would like to write [00,00,99,10] as
> hex values to my file. I was just wondering if there was a way to dump an
> entire struct to a file and then read it back later.
>
>
> Regards
> Ewald Horn
> Proprietor/Eienaar : Horn Labs
> Cell/Sel : 083 519 1615
> Website : http://www.hornlabs.co.za
> Email/E-pos : in...@ho...
>
>
>
>
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