How to read buffer in C?

mat2ag · 12-03-2007, 03:45 AM

Quote:

Originally Posted by obladioblada

paulsm4 is right.

I want to read structured data into an MPI buffer, so that I can send it with a single MPI_Bcast command? And then, at the receiver processor, I want to read the buffer.

I was trying to use following codes to write buffer:
int j;
j = 0;
for (i=0;i<n;i++)
{
j+= sprintf(fbuffer+j, "%d %f ",int_a[i], float_b[i]);
}

but I can NOT read it by using following code:

j = 0;
for (i=0;i<n;i++)
{
j+=sscanf(fbuffer+j, "%d %f ",&a,, &f1);
printf("%d %f ",a,f1);
}

And it will worse if there is char.

scanf family does not accept format as like printf, so you should read your int and float separately by tow following scanf.

raffica · 02-05-2009, 04:54 AM

Hi all,

I need to read a binary file where I previously stored double data.

The step are:
1. Open a file
2. Read binary data and convert them into double
3. Store them into a buffer

I need also know how many double data are.

Can someone help me please?

GazL · 02-05-2009, 10:45 AM

Quote:

Originally Posted by obladioblada

I was trying to use following codes to write buffer:
int j;
j = 0;
for (i=0;i<n;i++)
{
j+= sprintf(fbuffer+j, "%d %f ",int_a[i], float_b[i]);
}

printf("%d %f ",a,f1);
}

I'm still learning C, so forgive me if I've got this completely wrong, but as sprintf returns the length excluding the terminating /0, wouldn't that code result in the string terminator being overwritten in the next iteration of the loop resulting in one big string?

edit: Oh FFS! Sorry guys, didn't notice the thread necromancy.

paulsm4 · 02-05-2009, 12:15 PM

Well, like the tag line to that Stephen King movie goes, "Sometimes dead is better" ;-)

Anyway, hopefully this snippet answers your question:

Code:

/*
 * Sample output:
 *
 * j: 0, len: 3, fbuffer: ABC...
 *   0x41:A 0x42:B 0x43:C 0x0:
 * j: 3, len: 3, fbuffer: ABCDEF...
 *   0x41:A 0x42:B 0x43:C 0x44:D 0x45:E 0x46:F 0x0:
 */
#include <stdio.h>
#include <string.h>

#define MAX_STRING 80

char *s[] = {
  "ABC",
  "DEF"
};

void
dumpstr (const char *s)
{
  int i;
  printf ("  ");
  for (i=0; i <= strlen(s); i++)
    printf ("0x%x:%c ", s[i], s[i]);
  printf ("\n");
}

int
main (int argc, char *argv[])
{
  char buff[80];
  char *fbuffer = buff;
  int i, j = 0;
  for (i=0; i < 2; i++)
  {
    int len = sprintf(fbuffer+j, "%s", s[i]);
    printf ("j: %d, len: %d, fbuffer: %s...\n", j, len, fbuffer);
    dumpstr (buff);
    j += len;
  }
  return 0;
}

GazL · 02-05-2009, 05:24 PM

Thanks Paul. I can see that dumpstr function coming in very handy for debugging stuff.