loadlibrary - Load shared library into MATLAB software

Syntax

Description

loadlibrary('shrlib', 'hfile') loads the functions defined in header file hfile and found in shared library shrlib into MATLAB. You must select a supported C compiler and Perl must be available. To select a compiler, use the mex -setup command, described in Selecting a Compiler on Windows Platforms and Selecting a Compiler on UNIX Platforms. For an up-to-date list of supported compilers, see the Supported and Compatible Compilers Web page.

The hfile and shrlib file names are case sensitive. The name you use in loadlibrary must use the same case as the file on your system.

On Microsoft Windows systems, shrlib refers to the name of a Shared library (.dll) file. On Linux systems, it refers to the name of a shared object (.so) file. On Apple Macintosh systems, it refers to a dynamic shared library (.dylib). See File Extensions for Libraries for more information.

Note   loadlibrary does not support libraries generated by the MATLAB Compiler™ product.

loadlibrary('shrlib', @protofile) uses a prototype file protofile in place of a header file in loading the library shrlib. The string @protofile specifies a function handle to the prototype file. (See the description of Prototype Files below).

Note   The MATLAB Generic Shared Library interface does not support library functions that have function pointer inputs.

File Extensions for Libraries

If you do not include a file extension with the shrlib argument, loadlibrary attempts to find the library with either the appropriate platform MEX-file extension or the appropriate platform library extension (usually .dll, .so, or .dylib). For a list of file extensions, see Binary MEX-File Extensions.

If you do not include a file extension with the second argument, and this argument is not a function handle, loadlibrary uses .h for the extension.

loadlibrary('shrlib', ..., 'options') loads the library shrlib with one or more of the following options.

loadlibrary shrlib hfile ...
   addheader hfile1 ...
   addheader hfile2 ...      % and so on

Only the alias option is available when loading using a prototype file.

If you have more than one library file of the same name, load the first using the library file name, and load the additional libraries using the alias option.

loadlibrary shrlib hfile options is the command format for this function.

[notfound, warnings] = loadlibrary('shrlib', 'hfile') returns warning information from the shrlib library file. notfound is a cell array of the names of functions found in the header file hfile, or any header added with the addheader option, but not found in the shrlib library. warnings contains a single character array of warnings produced while processing the header file hfile.

Tips

How to Use the addheader Option

The addheader option enables you to add functions for MATLAB to load from those listed in header files included in the base header file (with a #include statement). For example, if your library header file contains the statement:

#include header2.h

then to load the functions in header2.h, use addheader in the call to loadlibrary:

loadlibrary libname libname.h addheader header2

You can use the addheader option with a header file that lists function prototypes for only the functions that are needed by your library, and thereby avoid loading functions that you do not define in your library. To do this, you might need to create a header file that contains a subset of the functions listed in large header file.

addheader Syntax

When using addheader to specify which functions to load, ensure that there are #include statements in the base header file for each additional header file in the loadlibrary call. For example, to use the following statement:

loadlibrary mylib mylib.h addheader header2

the file mylib.h must contain this statement:

#include header2.h

Prototype Files

When you use the mfilename option with loadlibrary, MATLAB generates a file of MATLAB commands called a prototype file. Use this file on subsequent calls to loadlibrary in place of a header file.

Note   The mfilename name must be different from the shrlib library name.

Like a header file, the prototype file supplies MATLAB with function prototype information for the library. You can make changes to the prototypes by editing this file and reloading the library.

Here are some reasons for using a prototype file, along with the changes you would need to make to the file:

• You want to make temporary changes to signatures of the library functions.

  Edit the prototype file, changing the fcns.LHS or fcns.RHS field for that function. This changes the types of arguments on the left hand side or right hand side, respectively.

• You want to rename some of the library functions.

  Edit the prototype file, defining the fcns.alias field for that function.

• You expect to use only a small percentage of the functions in the library you are loading.

  Edit the prototype file, commenting out the unused functions. This reduces the amount of memory required for the library.

• You need to specify a number of include files when loading a particular library.

  Specify the full list of include files (plus the mfilename option) in the first call to loadlibrary. This puts all the information from the include files into the prototype file. After that, specify just the prototype file.

• You want to use functions with a variable number of arguments.

  Create an alias function in a prototype file for each set of arguments you use to call the function.

Using loadlibrary on 64-Bit Platforms

MATLAB generates a thunk file, which is a compatibility layer to your 64-bit library. The name of the thunk file is:

BASENAME_thunk_COMPUTER.c

where BASENAME is either the name of the shared library or the mfilename, if specified. COMPUTER is the string returned by the computer function.

MATLAB compiles this file and creates the file:

BASENAME_thunk_COMPUTER.LIBEXT

where LIBEXT is the platform-dependent default shared library extension, for example, dll on Windows.

Examples

Load shrlibsample Example

Use loadlibrary to load the MATLAB sample shared library, shrlibsample:

addpath(fullfile(matlabroot,'extern','examples','shrlib'))
loadlibrary shrlibsample shrlibsample.h

Using alias Example

Load sample library shrlibsample, giving it an alias name of lib. Once you have set an alias, you need to use this name in all further interactions with the library for this session:

addpath(fullfile(matlabroot,'extern','examples','shrlib'))
loadlibrary shrlibsample shrlibsample.h alias lib

libfunctionsview lib

str = 'This was a Mixed Case string';
calllib('lib', 'stringToUpper', str)
ans =
   THIS WAS A MIXED CASE STRING
unloadlibrary lib

Using includepath Example

Load the library, specifying an additional path in which to search for included header files:

addpath(fullfile(matlabroot,'extern','examples','shrlib'))
loadlibrary('shrlibsample','shrlibsample.h','includepath', ...
            fullfile(matlabroot,'extern','include'));

Using Prototype Example

Load the libmx library and generate a prototype file containing the prototypes defined in header file matrix.h:

hfile = [matlabroot '\extern\include\matrix.h'];
loadlibrary('libmx', hfile, 'mfilename', 'mxproto')

dir mxproto.m
   mxproto.m

Edit the generated file mxproto.m and locate the function mxGetNumberOfDimensions. Give it an alias of mxGetDims by adding this text to the line before fcnNum is incremented:

fcns.alias{fcnNum}='mxGetDims';

Here is the new function prototype. The change is shown in bold:

fcns.name{fcnNum}='mxGetNumberOfDimensions'; 
fcns.calltype{fcnNum}='cdecl';
fcns.LHS{fcnNum}='int32'; 
fcns.RHS{fcnNum}={'MATLAB array'};
fcns.alias{fcnNum}='mxGetDims'; % Alias defined
fcnNum=fcnNum+1; % Increment fcnNum

Unload the library, and then reload it using the prototype file.

unloadlibrary libmx

loadlibrary('libmx', @mxproto)

Now call mxGetNumberOfDimensions using the alias function name:

y = rand(4, 7, 2);

calllib('libmx', 'mxGetDims', y)
ans =
     3

unloadlibrary libmx

See Also

computer | libfunctions | libisloaded | unloadlibrary