B&R PLC. Calculate new offset after write or how to write data to new line - file-io

Question

I have this program which creates file on USB stick. The problem is it is only saving one line (rewriting same line). I would need after each cycle it would write the data to new line . I think it has to do something with offset I need to calculate offset so it doesn't start from 0 every time. Here is the part of the code
10: DevLink_0.enable := TRUE;
DevLink_0.pDevice := ADR('Disk');
DevLink_0.pParam := ADR(cesta_k_USB);
DevLink_0();
IF DevLink_0.status =0 THEN
step :=20;
END_IF
20: FileCreate_0.enable := TRUE;
FileCreate_0.pDevice := ADR('Disk');
FileCreate_0.pFile := ADR('results.csv');
FileCreate_0();
IF FileCreate_0.status = 0 THEN
identification_file := FileCreate_0.ident;
offset :=0;
step :=30;
END_IF
IF FileCreate_0.status = fiERR_EXIST THEN
step :=25;
END_IF
25: FileOpen_0.enable := TRUE;
FileOpen_0.pDevice := ADR('Disk');
FileOpen_0.pFile := ADR('results.csv');
FileOpen_0.mode := FILE_W;
FileOpen_0();
IF FileOpen_0.status = 0 THEN
identification_file := FileOpen_0.ident;
offset := FileOpen_0.filelen;
step := 30;
END_IF
30: data:=INT_TO_STRING(y);
data:=INSERT(data,'$r$n',LEN(data));
FileWrite_0.enable := TRUE;
FileWrite_0.ident := identification_file;
FileWrite_0.pSrc := ADR(data);
FileWrite_0.len := LEN(data);
FileWrite_0.offset := offset;
FileWrite_0();
IF FileWrite_0.status = 0 THEN
step :=40;
END_IF
40: FileClose_0.enable := TRUE;
FileClose_0.ident := identification_file;
FileClose_0();
IF FileClose_0.status =0 THEN
IF save = FALSE THEN
step :=50;
ELSE
step := 25;
END_IF
END_IF
50: DevUnlink_0.enable := TRUE;
DevUnlink_0.handle := DevLink_0.handle;
DevUnlink_0();
IF DevUnlink_0.status =0 THEN
stav:= 0;
END_IF

Answer 1

As already mentioned in a comment, you will need to set the offset in the FileWrite FUB correspondingly.
I do this usually with the FileInfo FUB Guid 6eaf42f0-4ce5-44b7-95cb-275ae1c2fac5 in the AS help. It will tell you if the file exists already and also which size it has.
If it exists, the next step would be FileOpen, otherwise FileCreate.
Recently I have created a small project on GitLab which is, among other things, also appending a line to a file: https://gitlab.com/kirni/bur_robotic_sample/blob/master/bur_robotic_sample/Logical/Libraries/TeachLib/Teach.c
The code is in C, but I am sure you get the idea.
case stTEACH_INFO:
/*setup fub*/
this->fbInfo.enable = 1;
this->fbInfo.pDevice = (UDINT)inst->szDevice;
this->fbInfo.pName = (UDINT)inst->szFile;
this->fbInfo.pInfo = &this->Info;
//call fub
FileInfo(&this->fbInfo);
//fub is done..
if(this->fbInfo.status != ERR_FUB_BUSY)
{
//file exists -> open it and append code
if(this->fbInfo.status == ERR_OK)
{
//start writing to the end of the file
this->Offset = this->Info.size;
//open existing file
this->Step = stTEACH_OPEN;
}
//file does not exist -> create it and insert code
else if(this->fbInfo.status == fiERR_FILE_NOT_FOUND)
{
//start writing at the beginning of the file
this->Offset = this->Info.size;
//crete new file
this->Step = stTEACH_CREATE;
}
//error
else
{
//set error status and goto error state
inst->Status = this->fbInfo.status;
this->Step = stTEACH_ERROR;
}
//disable fub
this->fbInfo.enable = 0;
FileInfo(&this->fbInfo);
}
break;
case stTEACH_CREATE:
/*setup fub*/
this->fbCreate.enable = 1;
this->fbCreate.pDevice = (UDINT)inst->szDevice;
this->fbCreate.pFile = (UDINT)inst->szFile;
//call fub
FileCreate(&this->fbCreate);
//fub is done..
if(this->fbCreate.status != ERR_FUB_BUSY)
{
//success
if(this->fbCreate.status == ERR_OK)
{
this->Ident = this->fbCreate.ident;
//open existing file
this->Step = stTEACH_WRITE;
}
//error
else
{
//set error status and goto error state
inst->Status = this->fbCreate.status;
this->Step = stTEACH_ERROR;
}
//disable fub
this->fbCreate.enable = 0;
FileCreate(&this->fbCreate);
}
break;
case stTEACH_OPEN:
/*setup fub*/
this->fbOpen.enable = 1;
this->fbOpen.pDevice = (UDINT)inst->szDevice;
this->fbOpen.pFile = (UDINT)inst->szFile;
this->fbOpen.mode = fiREAD_WRITE;
//call fub
FileOpen(&this->fbOpen);
//fub is done..
if(this->fbOpen.status != ERR_FUB_BUSY)
{
//success
if(this->fbOpen.status == ERR_OK)
{
this->Ident = this->fbOpen.ident;
//open existing file
this->Step = stTEACH_WRITE;
}
//error
else
{
//set error status and goto error state
inst->Status = this->fbOpen.status;
this->Step = stTEACH_ERROR;
}
//disable fub
this->fbOpen.enable = 0;
FileOpen(&this->fbOpen);
}
break;
case stTEACH_WRITE:
/*setup fub*/
this->fbWrite.enable = 1;
this->fbWrite.ident = this->Ident;
this->fbWrite.offset = this->Offset;
this->fbWrite.pSrc = this->szLine;
this->fbWrite.len = this->Lenght;
//call fub
FileWrite(&this->fbWrite);
//fub is done..
if(this->fbWrite.status != ERR_FUB_BUSY)
{
//success
if(this->fbWrite.status == ERR_OK)
{
this->Ident = this->fbWrite.ident;
//Write existing file
this->Step = stTEACH_CLOSE;
}
//error
else
{
//set error status and goto error state
inst->Status = this->fbWrite.status;
this->Step = stTEACH_ERROR;
}
//disable fub
this->fbWrite.enable = 0;
FileWrite(&this->fbWrite);
}
break;
However this should also work with the filelen output of the FileOpen FUB - just the way you did it. I would suggest, that you set a brakepoint just before writing and check if the offset is set on the FUB properly.
I would also recommend, that you call each FUB after it was done, again with enable:=0 (like I did in my sample) i.e. disabling it. Some FUBs only update their inputs parameters on a positive edge on the enable, execute, start, etc. input command.
I hope this helps!