Writing bytes to a file

[tech]

Hi, I want to dump 1500 bytes at a time to a file as part of the
logger i am writing for my driver.
However i want to the bytes to appear as text but as hex value not
characters.
I also need to separate each block of 1500 bytes by a new line and a
sequence number which identifies each block.

The following sample code gives me text output

static std::ofstream FileOutput("dat a.out",std::ios ::out);
static std::ostringstr eam os;
unsigned char Data[1500];

os << SeqNo << std::endl;

for (int i = 0; i < BufferLength; ++i)
{
os << Data [i];

}

os << std::endl;

How do i format Data to appear as hex values

Fileoutput << os.str();

[tech]

Re: Writing bytes to a file

On Mar 12, 10:57 am, tech <naumansulai... @googlemail.com wrote:

Hi, I want to dump 1500 bytes at a time to a file as part of the
logger i am writing for my driver.
However i want to the bytes to appear as text but as hex value not
characters.
I also need to separate each block of 1500 bytes by a new line and a
sequence number which identifies each block.
>
The following sample code gives me text output
>
static std::ofstream FileOutput("dat a.out",std::ios ::out);
static std::ostringstr eam os;
unsigned char Data[1500];
>
     os << SeqNo << std::endl;
>
     for (int i = 0; i < BufferLength; ++i)
      {
        os <<  Data [i];
>
      }
>
   os << std::endl;
>
How do i format Data to appear as hex values
>
Fileoutput << os.str();

ok no problem worked how to do just cast the char to an int and

os << std::hex << (int)Data[i];

[Juha Nieminen]

Re: Writing bytes to a file

tech wrote:

static std::ofstream FileOutput("dat a.out",std::ios ::out);
static std::ostringstr eam os;
unsigned char Data[1500];
>
os << SeqNo << std::endl;
>
for (int i = 0; i < BufferLength; ++i)
{
os << Data [i];
>
}
>
os << std::endl;
>
How do i format Data to appear as hex values
>
Fileoutput << os.str();

Why use a stringstream when you can write directly to the output stream?

This may be do what you want:

FileOutput.fill ('0');
for (int i = 0; i < BufferLength; ++i)
{
FileOutput << std::setw(2) << std::setbase(16 ) << Data [i];
}

[tech]

Re: Writing bytes to a file

On Mar 12, 12:02 pm, Juha Nieminen <nos...@thanks. invalidwrote:

tech wrote:

static std::ofstream FileOutput("dat a.out",std::ios ::out);
static std::ostringstr eam os;
unsigned char Data[1500];

>

     os << SeqNo << std::endl;

>

     for (int i = 0; i < BufferLength; ++i)
      {
   os <<  Data [i];

>

      }

>

   os << std::endl;

>

How do i format Data to appear as hex values

>

Fileoutput << os.str();

>
  Why use a stringstream when you can write directly to the output stream?
>
  This may be do what you want:
>
  FileOutput.fill ('0');
  for (int i = 0; i < BufferLength; ++i)
  {
      FileOutput << std::setw(2) << std::setbase(16 ) << Data [i];
  }- Hide quoted text -
>
- Show quoted text -

Hi, that didn't work because the Data is unsigned char type and the
file is opened
in text mode then its not being formatted to hex for some reason.

My method
os << std::hex << (int)Data[i];

works but the conversion to int is taking too long so its affecting
the logging. Your'e right
about using the file stream direct though.

So what i want to do is write a unsigned char as a hex value to a file
opened in text mode
without converting to an int

[Juha Nieminen]

Re: Writing bytes to a file

tech wrote:

works but the conversion to int is taking too long so its affecting
the logging.

Are you sure it's the conversion to int that is taking too long, and
not something else?

Maybe try using std::fprintf() instead of std::ofstream.