R help - Jun 2006 - read file with readBin (the file was saved with a C-routine)

Hello!

I have problems with using of "readBin" to read files, which was
written in C with "fwrite". In the C-File there is the following Code:

fwrite(MyitINI,sizeof(itINItype),1,outfile);

where MyitINI is a structure of the following form

typedef struct{
 int  KernelFileSave;      /* Determined, if Systemmatrix saved or not.*/
 char KernelFileName[200]; /* A-Matrix name                            */
 char StartFileName[200];  /* Startguess (optional)                    */
 int XSamples;             /* No of samples on 1. axis of recon image  */
 int YSamples;             /* No of samples on 2. axis of recon image  */
 float DeltaX;             /* Sampling distance 1. axis of recon image */
 float DeltaY;             /* Sampling distance 2. axis of recon image */
 float Xmin;               /* 1. sample position 1.axis of recon image */
 float Ymin;               /* 1. sample position 2.axis of recon image */
 }  itINItype;

I thought the following use of "readBin" sould it do, but it
doesn't

KernelFileSave <- readBin( con, integer(), n=1, size=4 )
KernelFileName <- readBin( con, character(), n=1 )
StartFileName <- readBin( con, character(), n=1 )
XSamples <- readBin( con, integer(), n=1, size=4 )
YSamples <- readBin( con, integer(), n=1, size=4 )
DeltaX <- readBin( con, numeric(), n=1, size=4 )
DeltaY <- readBin( con, numeric(), n=1, size=4 )
Xmin <- readBin( con, numeric(), n=1, size=4 )
Ymin <- readBin( con, numeric(), n=1, size=4 )

I think there is a problem if I read the character. Have you any ideas ???

Thanks for help.
J?rn Schulz.
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On 6/28/2006 11:48 AM, J?rn Schulz wrote:
> Hello!
> 
> I have problems with using of "readBin" to read files, which was
written in C with "fwrite". In the C-File there is the following Code:
> 
> fwrite(MyitINI,sizeof(itINItype),1,outfile);
> 
> where MyitINI is a structure of the following form
> 
> typedef struct{
>  int  KernelFileSave;      /* Determined, if Systemmatrix saved or not.*/
>  char KernelFileName[200]; /* A-Matrix name                            */
>  char StartFileName[200];  /* Startguess (optional)                    */
>  int XSamples;             /* No of samples on 1. axis of recon image  */
>  int YSamples;             /* No of samples on 2. axis of recon image  */
>  float DeltaX;             /* Sampling distance 1. axis of recon image */
>  float DeltaY;             /* Sampling distance 2. axis of recon image */
>  float Xmin;               /* 1. sample position 1.axis of recon image */
>  float Ymin;               /* 1. sample position 2.axis of recon image */
>  }  itINItype;
> 
> I thought the following use of "readBin" sould it do, but it
doesn't
> 
> KernelFileSave <- readBin( con, integer(), n=1, size=4 )
> KernelFileName <- readBin( con, character(), n=1 )
You've written out 200 characters, but are only reading up to the first 
null.  I think you want readChar here, or you want to change the way you 
write the struct.
> StartFileName <- readBin( con, character(), n=1 )
Same here.
> XSamples <- readBin( con, integer(), n=1, size=4 )
> YSamples <- readBin( con, integer(), n=1, size=4 )
> DeltaX <- readBin( con, numeric(), n=1, size=4 )
> DeltaY <- readBin( con, numeric(), n=1, size=4 )
> Xmin <- readBin( con, numeric(), n=1, size=4 )
> Ymin <- readBin( con, numeric(), n=1, size=4 )
> 
> I think there is a problem if I read the character. Have you any ideas ???
> 
> Thanks for help.
> J?rn Schulz.
I would also worry about the alignment of the fields within the struct, 
though it is probably okay given that everything is a multiple of 4 
bytes long.

Duncan Murdoch

On Wed, 28 Jun 2006, J?rn Schulz wrote:
> Hello!
>
> I have problems with using of "readBin" to read files, which was
written in C with "fwrite". In the C-File there is the following Code:
>
> fwrite(MyitINI,sizeof(itINItype),1,outfile);
>
> where MyitINI is a structure of the following form
>
> typedef struct{
> int  KernelFileSave;      /* Determined, if Systemmatrix saved or not.*/
> char KernelFileName[200]; /* A-Matrix name                            */
> char StartFileName[200];  /* Startguess (optional)                    */
> int XSamples;             /* No of samples on 1. axis of recon image  */
> int YSamples;             /* No of samples on 2. axis of recon image  */
> float DeltaX;             /* Sampling distance 1. axis of recon image */
> float DeltaY;             /* Sampling distance 2. axis of recon image */
> float Xmin;               /* 1. sample position 1.axis of recon image */
> float Ymin;               /* 1. sample position 2.axis of recon image */
> }  itINItype;
>
> I thought the following use of "readBin" sould it do, but it
doesn't
>
> KernelFileSave <- readBin( con, integer(), n=1, size=4 )
> KernelFileName <- readBin( con, character(), n=1 )
> StartFileName <- readBin( con, character(), n=1 )
> XSamples <- readBin( con, integer(), n=1, size=4 )
> YSamples <- readBin( con, integer(), n=1, size=4 )
> DeltaX <- readBin( con, numeric(), n=1, size=4 )
> DeltaY <- readBin( con, numeric(), n=1, size=4 )
> Xmin <- readBin( con, numeric(), n=1, size=4 )
> Ymin <- readBin( con, numeric(), n=1, size=4 )
>
> I think there is a problem if I read the character. Have you any ideas ???
The help page points you to readChar, which seems more appropriate: you 
could also use raw().

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595