C/C++ for LJM - Windows, Mac, Linux

C/C++ examples for the LJM library. Also contains some header files:

• LJM_Utilities.h - contains useful functions

• stream/LJM_StreamUtilities.h - contains useful stream functions

• LabJackMModbusMap.h - contains declarations for register addresses, names, and types

Prerequisites

• A T-series LabJack Device

• LJM Library - Install the LJM Library

• C/C++ Compiler - We use Microsoft Visual Studio on Windows and gcc on macOS and Linux.

• Operating System - Windows, macOS, or Linux.

Subsections

Repository: Our latest example changes are available in our GitHub repository.

GitHub

Our latest example changes are available in our GitHub repository.

Instructions

1. Go to your device Quickstart Tutorial and follow the steps to install LabJack software and confirm basic operation.

2. Download/extract the .zip file attached at the top of this page.

3. Navigate to the extracted LabJackM folder.

4. Open and run .c/.cpp source files using your code editor of choice.

Windows

Newer versions of Visual Studio work with these .sln and .vcproj files, though you will need to run the automatic upgrade process when opening them.

For Visual Studio 2017, you may get the following error:

Error   C1083   Cannot open include file: 'stdio.h': No such file or directory

In this case, you need to switch the project SDK version from 8.1 to 10:

1. Open the Properties window for the project (e.g. in the Solution Explorer, right click on the project - not the solution)

2. Change Configuration Properties → General → Target Platform Version to something like 10.0.14393.0

Mac/Linux

On Mac/Linux, the .zip format unfortunately removes the execution permissions from the build scripts. To use the examples on Mac/Linux, you may need to apply executable permissions. For example:

tar zxvf C_C++_LJM_2019-05-20.zip cd C_C++_LJM_2019-05-20 chmod a+x make_all.sh basic/make.sh more/*/make.sh scons-local-2.5.1/scons.py

LJM Overview

With the LJM library, pretty much everything you might want to do with a device is accomplished by writing and/or reading some registers.  Look at the T-series Datasheet or the Modbus Map to determine what registers you need to write and read, then use eWriteName (or eWriteNames) to write the desired registers and eReadName (or eReadNames) to read the desired registers.  The following examples in the Basic folder are a great place to start:

• LJM_eWriteName Example

• LJM_eWriteNames Example

• LJM_eReadName Example

• LJM_eReadNames Example

• Write Read Loop with Config

Where is an example to do XYZ?

You will find lots of examples in this archive, but there is not an example for everything the LabJack can do.  The reason for this stems from the "Overview" section above.  Most operations simply involve writing and reading different registers, so you really just need examples that show you how to write and read any register.  If we had examples for every operation, they would just be copies of the example "Write Read Loop with Config" with different registers. The typical workflow to do almost anything beside stream is:

1. Look at the T-series Datasheet or the Modbus Map to determine what registers you need to write and read.

2. Use the Register Matrix in Kipling to test writing and reading your desired registers and confirm you see what you expect to see.  This step is optional and not always applicable.

3. Use eWriteName (or eWriteNames) to write the desired registers and eReadName (or eReadNames) to read the desired registers. Or just use "Write Read Loop with Config", which provides the basic structure used by many user applications.

Stream mode and other operations that don't fit in "Write Read Loop with Config" will usually have specific examples, and if something seems to be missing let us know.

Compiling

To compile a C or C++ program that uses LJM see the compilation instructions, which include instructions for compiling programs including:

• General instructions

• Visual Studio instructions

• Using included make.sh build scripts

• Using Xcode

Code Snippet

#include <stdio.h> #include <LabJackM.h> #include "LJM_Utilities.h" // Available in the C/C++ examples download. Provides the ErrorCheck function. int main() { int err, handle; double value = 0; const char * NAME = {"SERIAL_NUMBER"}; // Open first found LabJack err = LJM_Open(LJM_dtANY, LJM_ctANY, "LJM_idANY", &handle); ErrorCheck(err, "LJM_Open"); // Call LJM_eReadName to read the serial number from the LabJack. err = LJM_eReadName(handle, NAME, &value); ErrorCheck(err, "LJM_eReadName"); printf("eReadName result:\n"); printf(" %s = %f\n", NAME, value); // Close device handle err = LJM_Close(handle); ErrorCheck(err, "LJM_Close"); return LJME_NOERROR; }

File list

Github Repository