FREAD File Read Function
Section: Input/Ouput Functions
UsageReads a block of binary data from the given file handle into a variable of a given shape and precision. The general use of the function is
A = fread(handle,size,precision)
handle argument must be a valid value returned by the fopen
function, and accessable for reading. The
size argument determines
the number of values read from the file. The
size argument is simply
a vector indicating the size of the array
can also contain a single
inf dimension, indicating that FreeMat should
calculate the size of the array along that dimension so as to read as
much data as possible from the file (see the examples listed below for
more details). The data is stored as columns in the file, not
Alternately, you can specify two return values to the
in which case the second value contains the number of elements read
[A,count] = fread(...)
count is the number of elements in
The third argument determines the type of the data. Legal values for this
argument are listed below:
- 'uint8','uchar','unsigned char' for an unsigned, 8-bit integer.
- 'int8','char','integer*1' for a signed, 8-bit integer.
- 'uint16','unsigned short' for an unsigned, 16-bit integer.
- 'int16','short','integer*2' for a signed, 16-bit integer.
- 'uint32','unsigned int' for an unsigned, 32-bit integer.
- 'int32','int','integer*4' for a signed, 32-bit integer.
- 'single','float32','float','real*4' for a 32-bit floating point.
- 'double','float64','real*8' for a 64-bit floating point.
'float', the data is read in as single precision, but the output type is always
'double'. This behavior is consistent with Matlab. If you want the output type to match the input type (as was previous behavior in FreeMat), you must preface the precision string with a
'*'. Thus, the precision string
'*float'implies that data is read in as single precision, and the output is also single precision. The third option is to specify the input and output types explicitly. You can do this by specifiying a precision string of the form
'type1 => type2', where
'type1'is the input type and
'type2'is the output type. For example, if the input type is
'double'and the output type is to be a
'float', then a type spec of
'double => float'should be used.
ExampleFirst, we create an array of
512 x 512Gaussian-distributed
floatrandom variables, and then writing them to a file called
--> A = float(randn(512)); --> fp = fopen('test.dat','w'); --> fwrite(fp,A); --> fclose(fp);
Read as many floats as possible into a row vector
--> fp = fopen('test.dat','r'); --> x = fread(fp,[1,inf],'float'); --> fclose(fp); --> who x Variable Name Type Flags Size x double [1 262144]
x is a
double array. This behavior is new to FreeMat 4.
Read the same floats into a 2-D float array.
--> fp = fopen('test.dat','r'); --> x = fread(fp,[512,inf],'float'); --> fclose(fp); --> who x Variable Name Type Flags Size x double [512 512]
To read them as a single precision float array, we can use the following form:
--> fp = fopen('test.dat','r'); --> x = fread(fp,[512,inf],'*float'); --> fclose(fp); --> who x Variable Name Type Flags Size x single [512 512]