compile a foreign .c file

**TobiasMiller** · 05-04-2022

Hello,

I am new to C programming and tried using the Simple Open EtherCAT library (SOEM) on a raspberry Pi. The language used is C.

I pulled the github repository from here (GitHub - OpenEtherCATsociety/SOEM: Simple Open Source EtherCAT Master) on my raspberry Pi. Then I built it as described in the README.md. The file path on my raspberry is now: /home/raspberrypi/SOEM.

I then connected an EtherCAT slave (to be precise, I connected 3: EK1100, EL1809 and EL2809) and then have run the simple_test executable (can be found in: /home/raspberrypi/SOEM/build/test/linux/simple_test) which worked fine. The output I got was without errors and the slave devices were detected.

Then I tried to programm my first own script which should make use of the SOEM functionalities (such as reading out the slaves PDO data). In the folder SOEM there is a simple_test.c file, which can be modified. When compiled, this file should do the exact same thing as the executable simple_test (which was described previously).

However, when I tried compiling the simple_test.c file using
gcc simple_test.c -o simple_test
in the terminal window, it throws an error saying:
fatal error: osal.h: No such file or directory
#include "osal.h"

The error should come from the fact that the program to be compiled does not know where the associated .h files are located. These are mostly under home/raspberrypi/SOEM/soem (however there are other files such as .o files in a different location).

My question is: How do I just manage to tell the program where the linked files are located? Do I have to specify the full file path every time I use the #include "..." command? If I do that, the compilation still throws errors because the needed functions are not found.

Thank you in advance!
Best regards,
Tobias

**rstanley** · 05-04-2022

Did the installation of the SOEM library install any header files in the "/usr/local/include/" or "/usr/include/" directories, then you should include them as

Code:

#include <header.h>
// Not as:
#include "header.h"

Otherwise, run your compile command as:

Code:

gcc -I /path/to/headers/ simple_test.c -o simple_test

<header.h> indicates a predefined include path. "header.h" indicates the current directory by default, unless you sue the "-I /path/" gcc option.

**john.c** · 05-04-2022

You need to tell gcc where the include files are with the -I flag:
-I/path/to/include/files
You need to tell gcc where the library files (.a or .so files) are with the -L flag:
-L/path/to/library/code
And you need to tell it which library file(s) to use with the -l (lowercase L) flag:
-lLIBRARY_FILE_NAME_WITHOUT_EXTENSION

So something like this (note that the -l flag goes last):
gcc -o mycode -I/path/to/include/files -L/path/to/library/code mycode.c -llibrary

**TobiasMiller** · 05-04-2022

Originally Posted by rstanley

Did the installation of the SOEM library install any header files in the "/usr/local/include/" or "/usr/include/" directories

Thank you for your response! Also big thanks to john.c
The installation didn't seem to have installed any header files in the directiories mentioned above. So I guess, I have to define the directory paths manually.

Unfortunately, there are several .h files under different paths. For example, one is in the /home/raspberrypi/SOEM/osal folder, another is under /home/raspberrypi/SOEM/oshw, etc.

Do I then have to manually specify all these paths when compiling?

**john.c** · 05-04-2022

Do I then have to manually specify all these paths when compiling?

You could pass -I/home/raspberrypi/SOEM and then specify header files like:

Code:

#include "osal/whatever"
#include "oshw/whatever"

**TobiasMiller** · 05-05-2022

@john.c

I now tried the following code:

gcc simple_test.c -o simple_test -I/home/raspberrypi/SOEM/osal -I/home/raspberrypi/SOEM/osal/linux -I/home/raspberrypi/SOEM/oshw/linux -L/home/raspberrypi/SOEM/osal/linux/osal.c -L/home/raspberrypi/SOEM/oshw/linux/oshw.c

But this threw out the following error code:
/usr/bin/ld: /tmp/cclThXAw.o: in function `simpletest':
simple_test.c: (.text+0x34): undefined reference to `ec_init'
/usr/bin/ld: simple_test.c: (.text+0x54): undefined reference to `ec_config_init'
/usr/bin/ld: simple_test.c: (.text+0x7c): undefined reference to `ec_config_map'
/usr/bin/ld: simple_test.c: (.text+0x80): undefined reference to `ec_configdc'
/usr/bin/ld: simple_test.c: (.text+0x98): undefined reference to `ec_statecheck'
/usr/bin/ld: simple_test.c: (.text+0x1b4): undefined reference to `ec_send_processdata'
/usr/bin/ld: simple_test.c: (.text+0x1bc): undefined reference to `ec_receive_processdata'
/usr/bin/ld: simple_test.c: (.text+0x1c4): undefined reference to `ec_writestate'
/usr/bin/ld: simple_test.c: (.text+0x1d0): undefined reference to `ec_send_processdata'
/usr/bin/ld: simple_test.c: (.text+0x1d8): undefined reference to `ec_receive_processdata'
/usr/bin/ld: simple_test.c: (.text+0x1e8): undefined reference to `ec_statecheck'
/usr/bin/ld: simple_test.c: (.text+0x240): undefined reference to `ec_send_processdata'
/usr/bin/ld: simple_test.c: (.text+0x248): undefined reference to `ec_receive_processdata'
/usr/bin/ld: simple_test.c: (.text+0x340): undefined reference to `osal_usleep'
/usr/bin/ld: simple_test.c: (.text+0x378): undefined reference to `ec_readstate'
/usr/bin/ld: simple_test.c: (.text+0x444): undefined reference to `ec_ALstatuscode2string'
/usr/bin/ld: simple_test.c: (.text+0x49c): undefined reference to `ec_writestate'
/usr/bin/ld: simple_test.c: (.text+0x4b4): undefined reference to `ec_close'
/usr/bin/ld: simple_test.c: (.text+0x4e4): undefined reference to `ec_slavecount'
/usr/bin/ld: simple_test.c: (.text+0x4f8): undefined reference to `ec_slave'
/usr/bin/ld: simple_test.c: (.text+0x4fc): undefined reference to `ec_group'
/usr/bin/ld: simple_test.c: (.text+0x528): undefined reference to `ec_DCtime'
/usr/bin/ld: /tmp/cclThXAw.o: in function `ecatcheck':
simple_test.c: (.text+0x620): undefined reference to `ec_readstate'
/usr/bin/ld: simple_test.c: (.text+0x74c): undefined reference to `ec_writestate'
/usr/bin/ld: simple_test.c: (.text+0x7c8): undefined reference to `ec_writestate'
/usr/bin/ld: simple_test.c: (.text+0x810): undefined reference to `ec_reconfig_slave'
/usr/bin/ld: simple_test.c: (.text+0x8b0): undefined reference to `ec_statecheck'
/usr/bin/ld: simple_test.c: (.text+0x99c): undefined reference to `ec_recover_slave'
/usr/bin/ld: simple_test.c: (.text+0xa98): undefined reference to `osal_usleep'
/usr/bin/ld: simple_test.c: (.text+0xab0): undefined reference to `ec_group'
/usr/bin/ld: simple_test.c: (.text+0xab8): undefined reference to `ec_slave'
/usr/bin/ld: simple_test.c: (.text+0xad4): undefined reference to `ec_slavecount'
/usr/bin/ld: /tmp/cclThXAw.o: in function `main':
simple_test.c: (.text+0xb18): undefined reference to `osal_thread_create'
/usr/bin/ld: simple_test.c: (.text+0xb4c): undefined reference to `ec_find_adapters'
/usr/bin/ld: simple_test.c: (.text+0xb8c): undefined reference to `ec_free_adapters'
collect2: error: ld returned 1 exit status

I guess I -L-flagged the wrong library files. But I don't have any .a or .so files, only .c.o files found under /home/raspberrypi/SOEM/build/CMakeFiles/soem.dir.
Should I use these? Is compiling code any different with CMake?

**TobiasMiller** · 05-05-2022

I have also found another folder under the following path:

/home/raspberrypi/SOEM/build/test/linux/simple_test/CMakeFiles/simple_test.dir

in this folder, there are several files like "DependInfo.cmake" or "depend.make", "depend.internal", etc.
Could I make use of these to compile my code more easily?

**rstanley** · 05-05-2022

First, go back and insure that you compiled and installed SOEM correctly with no errors reported. Then examine the Tutorial.

Good luck!

**john.c** · 05-05-2022

Did you execute sudo make install from the build directory?
If not, do so.

**john.c** · 05-05-2022

Once you've installed it, you should refer to the header files in your source code like this:

Code:

#include <soem/osal.h>
#include <soem/oshw.h>

Then compile like this:

Code:

gcc yourprog.c -o yourprog -lsoem

(Note that -l is a lowercase L)

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