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<html>
<head>
<title>IEEEIO C Interface</title>
</head>
<body bgcolor="#F0F0F0">
<table><tr>
<td><img src="Images/info.gif"></td>
<td><h1>ANSI and K&R C</h1></td>
</tr></table>
<hr>
<h1>Using the C Interface</h1>
To use the C interface, you must include the
headers <b>IO.h</b> and <b>IEEEIO.h</b>. By default the headers
are treated as K&R C (eg. no prototypes) because that is the
default of for many workstation C compilers. To enable the ANSI
C prototypes compile with -DANSI or use <b>#define ANSI</b> in
your source files before you include the <b>IO.h</b> and
<b>IEEEIO.h</b> headers. If you only require
the IEEEIO interface, you link only with <b>libieeeio.a</b> using
<code>-L$IEEE_DIRECTORY/lib -lieeeio</code><p>
If you also want HDF support you must also include the header
<b>HDFIO.hh</b> and link with <b>libhdfio.a</b> and
the usual complement of HDF libraries using
<code>-L$HDF_DIRECTORY/lib -L$IEEE_DIRECTORY/lib -lhdfio -lieeeio -lmfhdf -ldf -ljpeg -lz</code><p>
<hr>
<h1>C Subroutines</h1>
<UL>
<LI><a href="#Opening">Opening and Closing Datafiles</a>
<LI><a href="#Writing">Writing Datasets</a>
<LI><a href="#Reading">Reading Datasets</a>
<LI><a href="#Seeking">Random Access to Datasets
<i>(Seeking)</i></a>
<LI><a href="#WriteAttribs">Writing Attributes</a>
<LI><a href="#ReadAttribs">Reading Attributes</a>
<LI><a href="#WriteAnn">Writing Annotations</a>
<LI><a href="#ReadAnn">Reading Annotations</a>
<LI><a href="#ReadWriteChunk">Writing and Reading in Chunks</a>
</UL>
<hr>
<a name="Opening"><h2>Opening</h2></a>
Just like the familiar <b>FILE*</b> type for C stdio operations, all
IEEEIO operations require a file handle. The type of this handle is
IOFile (and 8-byte integer number). The <b>IEEEopen()</b> and
<b>HDFIOopen()</b>
routines are used to create this handle and the IOclose() subroutine can
be used to close file handles of either type.<p>
<b>ANSI C Prototype</b><br>
<code>IOFile IEEEopen(char *filename,char *accessmode);</code><br>
<DL>
<DT><i>filename</i>:
<DD>The name of the IEEEIO data file to
open. The typical extension for these files is <i>.raw</i>
<DT><i>accessmode</i>:
<DD>The accessmode for the file. This is
one of 3 different access modes
<UL>
<LI><b>"read"</b>:<i>Opens a file in read-only mode. This
can also be selected using any of the standard fopen()
modes; "r" and "rb"</i>
<LI><b>"write"</b>:<i>Opens a file in write-only mode. If the
file does not exist, it will be created. If it does exist, it will be
truncated. This
can also be selected using any of the standard fopen()
modes; "w","wb","w+","w+b", and "wb+"</i>
<LI><b>"append"</b>: <i>Opens a file in read/write mode. The file
pointer is automatically placed at the end of the file for appending,
but random-access read operations are allowed as well.This
can also be selected using any of the standard fopen()
modes; "a","ab","a+","a+b", and "ab+"</i>
</UL>
</DL>
After you open the file handle you can use the same set of
subroutines for operations on the file regardless of whether the
file is HDF or IEEEIO. The libraries manage all of this internally. So
the open step is the only thing that is important to differentiating
between your HDF and IEEEIO files.
There are plans, for example, to have a SocketIO system
that allows the data to be written out to a TCP socket instead of to a
file for real-time simulation-visualization systems. There are also
plans to use this interface to drive an existing Parallel IO
system.<p><br>
<pre>
/* write an IEEEIO file */
IOFile writer = IEEEopen("datafileout.raw","write");
/* write an HDF file */
IOFile writer = HDFIOopen("datafileout.raw","w"); /* "w" is also valid */
/* another way to open for writing */
IOFile writer = IEEEopenWrite("datafileout.raw");
/* open HDF file for reading */
IOFile reader = HDFIOopen("datafilein.raw","read");
/* another way to open an HDF file for reading */
IOFile reader = HDFIOopenRead("datafileout.raw");
/* another way to open an IEEEIO file for reading */
IOFile reader = IEEEopenRead("datafileout.raw");
</pre><p>
You can test if the file was opened successfully using the
IOisValid() function.<br>
<pre>
IOFile fileID = IEEEopen("datafileout.raw","write");
if(!IOisValid(fileID))
puts("The file you specified does not exist or is not in a
readable format");
</pre><br>
To close the file, you simply use IOclose.
<pre>
IOclose(IOFile filehandle);
</pre>
<hr>
<a name="Writing"><h2>Writing</h2></a>
To write data you simply use the method write().
<p><b>ANSI C Prototype</b><br>
<code>int IOwrite(IOFile filehandle,int numbertype,int rank,int
*dimensions,void *data);</code>
<DL>
<DT><i>filehandle</i>
<DD>An open filehandle for the datafile.
<DT><i>numbertype</i>:
<DD>The type of the data being stored
<i>(<a href="DataTypes.html">datatype definition</a>)</i>.
It can be one of
<UL>
<LI><b>FLOAT32</b><br><i>32-bit single-precision IEEE
float</i>
<LI><b>FLOAT64</b><br><i>64-bit double-precision IEEE
float</i>
<LI><b>STRING</b><br><i>Character string. This is
null-terminated automatically by the API. This is
interpreted differently from the <b>byte</b> datatype
which is raw data.</i>
<LI><b>INT8</b><br><i>byte</i>
<LI><b>INT16</b><br><i>16-bit short integer</i>
<LI><b>INT32</b><br><i>32-bit standard integer</i>
<LI><b>INT64</b><br><i>64-bit long integer. (note: this is not
availible on the Intel/Windows platform because it
does not allow 64-bit integers)</i>
<LI><b>UINT8</b><br><i>unsigned character</i>
<LI><b>UINT16</b><br><i>unsigned 16-bit short integer</i>
<LI><b>UINT32</b><br><i>unsigned 32-bit standard integer</i>
<LI><b>UINT64</b><br><i>unsigned 64-bit long
integer. (note: this is not availible on the
Intel/Windows platform)</i>
</UL>
<DT><i>rank</i>
<DD>Number of dimensions of the dataset
<DT><i>dimensions</i>:
<DD>An array of <i>rank</i> integers that give the dimensions of
the dataset
<DT><i>data</i>:
<DD>Your data array.
</DL>
So to write a sample array of data.
<pre>
float myarray[40][50][60]; /* our bogus data array */
int i,rank=3;
int dims[3]={60,50,40}; /* notice these are reversed. */
/* this is because ieeeio assumes f77 order for data
and c/c++ use exactly the opposite ordering for data in */
memory.
IOFile writer=IEEEopen("datafile.raw","write"); /* create a outfile */
for(i=0;i<ndatasets;i++){
. . . . computation . . .
IOwrite(writer,FLOAT32,rank,dims,myarray); /* write a dataset */
. . . . you can write as many datasets as you want
}
IOclose(writer); /* then close the file */
</pre>
<hr>
<a name="Reading"><h2>Reading Data</h2></a>
Reading is a two step process. First you get information on
the size and type of the data you intend to read. This allows
you to allocate an array of the proper size and type for the
reading. Then you actually read the data into a pre-allocated
array. The methods for this are <b>IOreadInfo()</b> and
<b>IOread()</b>.<p>
<b>ANSI C Prototype</b><br>
<code>int IOreadInfo(IOFile filehandle,int *numbertype,int *rank,int
*dims,int maxdims);</code><p>
<DL>
<DT><i>filehandle</i>
<DD>A filehandle open for reading or appending.
<DT><i>numbertype</i>:
<DD>The type of the data being stored
<i>(<a href="DataTypes.html">datatype definition</a>)</i>.
It can be one of
<UL>
<LI><b>FLOAT32</b><br><i>32-bit single-precision IEEE float</i>
<LI><b>FLOAT64</b><br><i>64-bit double-precision IEEE float</i>
<LI><b>INT8</b><br><i>byte</i>
<LI><b>INT16</b><br><i>16-bit short integer</i>
<LI><b>INT32</b><br><i>32-bit standard integer</i>
<LI><b>INT64</b><br><i>64-bit long integer. (note: this is not
availible on the Intel/Windows platform)</i>
<LI><b>UINT8</b><br><i>unsigned character</i>
<LI><b>UINT16</b><br><i>unsigned 16-bit short integer</i>
<LI><b>UINT32</b><br><i>unsigned 32-bit standard integer</i>
<LI><b>UINT64</b><br><i>unsigned 64-bit long integer. (note: this is not availible on the Intel/Windows platform)</i>
</UL>
<DT><i>rank</i>
<DD>Number of dimensions of the dataset
<DT><i>dimensions</i>:
<DD>An array of <i>rank</i> integers that give the dimensions
of the dataset
<DT><i>maxdims</i>:
<DD>The maximum size of the dimensions array you given it.
This prevents array overruns if the dataset has more
dimensions than you were anticipating. It can be any positive
integer.
</DL>
This retrieves information about the datatype, rank,
and dimensions of the dataset to be retrieved.
By default the maximum size of the dimensions array is 3,
but you can set it to be larger.<p>
<b>ANSI C Prototype</b><br>
<code>
int IOread(IOFile filehandle,void *data);
</code><p>
This actually reads the dataset into the preallocated array
<i>data</i>.<p>
Another useful utility function is IOsizeOf() which returns the
number of bytes in a give IO datatype in manner analogous to the
standard C sizeof() operator.
So for instance, to read a simple dataset, you would do
<pre>
int rank;
int numbertype;
int dims[3];
float *data; /* assumes float data */
IOFile infile = IEEEopen("dataset.raw","read");
IOreadInfo(infile,&numbertype,&rank,dims);
/* OK, we are assuming a 3D IO::Float32 array,
but you can be more sophisticated... */
data = (float*)malloc(IOnBytes(numbertype,rank,dims));
/* nBytes() is a convenience function... you could also use
data = (float*)malloc(dims[0] * dims[1] * dims[2] * IOsizeOf(numbertype)); */
IOread(infile,data); /* read in the data */
</pre><p>
Since multiple datasets can be stored in a file, you can
retrieve them in the order they were written <i>(there is a <a
href="#Seeking">seek()</a> function that allows random access as
well)</i>. The method <b>readInfo()</b> implies reading the next
dataset stored in the file. The method <b>nDatasets()</b> tells how
many datasets are in a file. So typically if you want to read all
datasets in a file in order, you would use code similar to;
<pre>
IOFile infile = IEEEopen("dataset.raw","r");
for(int i=0;i< IOnDatasets(infile);i++){
.....lots of code....
IOreadInfo(infile,&numbertype,&rank,dims); /* increments to next dataset */
.....more code....
}
</pre>
<hr>
<a name="Seeking"><h2>Random Access to Datasets
<i>(Seeking)</i></h2></a>
You can select specific datasets in a file using the seek()
method.<p>
<b>ANSI C Prototype</b>
<code>int IOseek(IOFile filehandle,int index)</code>
<DL>
<DT><i>filehandle</i>:
<DD>Handle to a file open for reading.
<DT><i>index</i>:
<DD>The index of the dataset you want to read from. This can
be any number from 0 to (number_of_datasets - 1).
</DL>
<hr>
<a name="WriteAttribs"><h2>Writing Attributes</h2></a>
Attributes allow you to attach extra information to each
dataset stored in the file. Each attribute has a name and an
array of data (of any of the standard IO datatypes) stored with
it. These attributes can be retrieved by name or by integer
index in the order in which they were stored. A typical
attribute would typically be parameters that describe the grid
or the data like, "origin" which would be the 3-vector of floats
which locates of the origin of a grid in 3-space. The method
used to write these attributes is <b>IOwriteAttribute()</b>.<p>
<b>ANSI C Prototype</b><br>
<code>
int IOwriteAttribute(IOFile filehandle,char *name,int numbertype,int
length,void *data)
</code><p>
<DL>
<DT><i>filehandle</i>
<DD>An open filehandle for the datafile.
<DT><i>name</i>:
<DD>Name of the attribute (like "origin" or "coordinates")
<DT><i>numbertype</i>:
<DD>The type of the data array associated with the attribute
<i>(<a href="DataTypes.html">datatype definition</a>)</i>
<DT><i>length</i>:
<DD>The number of elements in the data array.
<DT><i>data</i>:
<DD>The attribute data.
</DL><p>
So to write an attribute named <i>origin</i> along with a
3-vector float for the coordinates of the origin, you would use;
<pre>
float origin[3]={5.1,0.3,0.5};
/* and assuming the file is already open for writing
the following attribute will be attached to the last
written dataset. (you must have write data before adding
attribs) */
IOwriteAttribute(writer,"origin",FLOAT32,3,origin);
</pre>
<hr>
<a name="ReadAttribs"><h2>Reading Attributes</h2></a>
The attributes can be retrieved in the order they were written
or they can be retrieved by their name. To retrieve the
attributes in order, you would utilize the <b>IOnAttributes()</b>
method to determine how many attributes are attached,
<b>IOreadIndexedAttributeInfo()</b> to get the size and type of the
attribute based on its index (<i>use IOreadAttributeInfo() to get size
and type for the attribute based on its name</i>),
and <b>IOreadAttribute()</b> to read the attribute
data.<p>
<b>ANSI C Prototype</b><br>
<code>int IOnAttributes()</code><p>
<DL>
<DT><i>filehandle</i>
<DD>An open filehandle for the datafile.
<DT><i>returnvalue</i>:
<DD>Number of attributes in the file
</DL><p>
<b>ANSI C Prototype</b><br>
<code>int IOreadIndexedAttributeInfo(IOFile filehandle,int index,char *name,int *numbertype,int *length,int maxnamelength);
</code>
<DL>
<DT><i>filehandle</i>
<DD>An open filehandle for the datafile.
<DT><i>index</i>:
<DD>The index of the attribute which can be 0 to (nattributes-1)
<DT><i>name</i>:
<DD>A buffer in which the name of the attribute will be placed.
<DT><i>numbertype</i>:
<DD>The type of the attribute data
<i>(<a href="DataTypes.html">datatype definition</a>)</i>
<DT><i>length</i>:
<DD>The number of elements in the attribute data.
<DT><i>maxnamelength</i>:<DD>The maximum size of a name that can be
stored in the <b>name</b> buffer. It can be any positive integer.
</DL>
<p>
<b>ANSI C Prototype</b><br>
<code>int IOreadAttribute(IOFile filehandle,int index,void
*data);</code>
<DL>
<DT><i>filehandle</i>
<DD>An open filehandle for the datafile.
<DT><i>index</i>:
<DD>The index of the attribute data to read
<DT><i>data</i>:
<DD>The array into which the attribute data is copied.
</DL>
So for example, to read the attributes in order, you can use
<pre>
for(int i=0;i<IOnAttributes(infile);i++){
char name[128];
int length,datatype;
...
IOreadIndexedAttributeInfo(infile,i,name,&datatype,&length,128);
... allocate some data for storage
IOreadAttribute(infile,i,data);
}
</pre><p>
The attributes can also be retrieve by name. In fact, the is
the most likely way you will use the attributes interface. The
<b>IOreadAttributeInfo()</b> method is overloaded to allow retrieval by
name as
well. It returns the index of the attribute if one is found with a
matching name: it returns -1 if one is not found.
<p><b>ANSI C Prototype</b><br>
<code>
int IOreadAttributeInfo(char *name,int *numbertype,int *length);
</code>
<DL>
<DT><i>filehandle</i>
<DD>An open filehandle for the datafile.
<DT><i>returnvalue</i>:
<DD>The index of the attribute if found or -1 if no attribute with
matching name is found.
<DT><i>name</i>:
<DD>The name of the attribute to find.
<DT><i>numbertype</i>:
<DD>Returns the numbertype of the stored attribute data
<i>(<a href="DataTypes.html">datatype definition</a>)</i>
<DT><i>length</i>:
<DD>he length of the stored attribute data.
</DL>
So a typical use of this interface would be to find an attribute
named "origin" and retrieve its data if it exists.
<pre>
int index = IOreadAttributeInfo(infile,"origin",&datatype,&length);
if(index>=0) /* the attribute exists */
IOreadAttribute(infile,index,data);
else
puts("The attribute origin could not be found");
</pre>
</pre>
<hr>
<a name="WriteAnn"><h2>Writing Annotations</h2></a>
An annotation is a text string which can be used to
describe a dataset. To write an annotation, you use the
writeAnnotation() method.<p>
<b>ANSI C Prototype</b><br>
<code>
int IOwriteAnnotation(IOFile filehandle,char *annotationtext)
</code>
<DL>
<DT><i>filehandle</i>
<DD>An open filehandle for the datafile.
<DT><i>annotationtext</i>:
<DD>A null terminated string of the annotation text
</DL>
The annotation will be attached to the last written dataset.
You can store more than one annotation per dataset and the
annotations can be of arbitrary length.<p>
<hr>
<a name="ReadAnn"><h2>Reading Annotations</h2></a>
The annotations are stored in the order they are written. The
method <b>nAnnotations()</b> is used to find out how many
attributes are attached to a dataset. The method
<b>readAnnotationInfo()</b> is used to find the length of the
annotation and <b>readAnnotatin()</b> reads the actual
annotation text.<p>
<b>ANSI C Prototype</b><br>
<code>
int IOnAnnotations(IOFile filehandle);
</code>
<DL>
<DT><i>filehandle</i>
<DD>An open filehandle for the datafile.
<DT><i>returnvalue</i>:
<DD>Number of annotations attached to current dataset.
</DL><p>
<b>ANSI C Prototype</b><br><code>
IOreadAnnotationInfo(IOFile filehandle,int index,int *length)
</code>
<DL>
<DT><i>filehandle</i>
<DD>An open filehandle for the datafile.
<DT><i>index</i>:
<DD>Index of the annotations which can be 0 to (nannotations-1)
<DT><i>length</i>:
<DD>Length in characters of the annotation. This includes the
null-terminating character.
</DL>
<hr>
<a name="ReadWriteChunk"><h2>Writing and Reading in Chunks</h2></a>
For distributed-memory programming paradigms like HPF, MPI, or
PVM, it is often not unfeasible to write data to disk in a
single operation. For this reason, a <i>chunking</i> interface
is provided which allows you to write data in blocks to the
disk.<p>
To begin a chunk writing operation, you must first reserve a
data chunk in the file. This is accomplished using <b>IOreserveChunk()</b>
<b>ANSI C Prototype</b><br>
<code>
int IOreserveChunk(IOFile filehandle,int datatype,int rank,int *dims);
</code><p>
Once space has been allocated in the datafile, you can write
blocks of data specified by their dimensions and origin using
<b>IOwriteChunk()</b>
<b>ANSI C Prototype</b><br>
<code>
int IOwriteChunk(IOFile filehandle,int *dims,int *origin,void *data);
</code><p>
Likewise, it is possible to read chunks from the disk as
well. No special procedure is required to select a record to
read in chunks. Simply use <a href="#Reading">IOreadInfo()</a>
to get the dimensions and
type of the dataset and then use <b>IOreadChunk()</b> in place
of <b>IOread()</b> in order to read-in the data.
<b>ANSI C Prototype</b><br>
<code>
int IOreadChunk(IOFile filehandle,int *dims,int *origin,void *data);
</code><p>
<hr>
<address><a href="mailto:jshalf@suttung.aei-potsdam.mpg.de">John
Shalf</a></address>
<!-- Created: Mon Apr 7 12:52:52 MDT 1997 -->
<!-- hhmts start -->
Last modified: Thu Feb 4 21:58:57 CST 1999
<!-- hhmts end -->
</body>
</html>
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