Skip to Content

Register Login

Industry Online Support

Technical Forum

Navigation

SO, how do you convert ARRAY[1..n] of CHAR to STRING? I know a work-around but why does it have to be so hard?

Created by: 0_Einstein at: 7/29/2010 10:57 PM (16 Replies)

Rating (5)

Thanks 8

Result pages:: |; 1 | 2; |

17 Entries

Entries per page: 10 | all

7/29/2010 10:57 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/23/2024 Posts: 15531 Rating: (2462)	Ok, as I develop an application with RS485 communications using a simple ASCII protocol with some networked drives. Some of the capabilities are quite nice, while others are annoying in the way they simply are not there or obvious, or worse where the documentation differs from the actual program entry. I have a case where I need tosearch for a character (received via RS485) within a 'valid string'. Specificaly, each drive sends ASCII messages with their address as the first character. As part of parsing and validating the received message, grab the first character from the buffer, copy it to a FC/FB input parameter, then inside the FC/FB try to compare it to a string, say '23456'. The character MUST be a string for the FIND function to work despite the documentation stating it allows for a CHAR for the comparison. Since there is no native CHAR -> STRING conversion, I had to create a FC/FB to accept the char, and return a STRING[1]. Don't get me started on how to copy an array of CHAR to a STRING.... That's also annoying in how it must be accomplished. I cannot even create an array index from a tag. For example, it would be nice to walk through an array (a loop), grab the value and append to a string. #temp_array[#counter] That doesn't appear to be allowed inside the FC/FB. </rant> SO, how do you convert ARRAY[1..n] of CHAR to STRING? I know a work-around but why does it have to be so hard? --- well I thought I had a work-around.... --- Splitted from bugs in S7 1200.
	Last edited by: O_Moderator at: 7/30/2010 10:27 AM new subject after splitting Last edited by: huggy_d1 at: 7/29/2010 11:34 PM science guy
Suggestion To thank Quote Answer

7/30/2010 12:13 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 1/13/2025 Posts: 4391 Rating: (1462)	Hi, if youwork withabsolute addres(without simbolic address only) maybe your task would be light... the struct of a STRING is [max size of the string - as byte], [actual size of the string - as byte], [array of chars]. You have alread the last two information . So, the tip is place create a STRING with a pre defined lengh (in a DB), so the first variable was alread filled. Then, place your data from the second byte of these DB (using absolut addressing).
	Denilson Pegaia Siemens Industry Sector Technical Support
Suggestion To thank Quote Answer

7/30/2010 2:52 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/23/2024 Posts: 15531 Rating: (2462)	Yes, for the trivial case of a single char->string the suggestion is precisely how I accomplished it. How does one loop through the addresses? Is indirect addressing allowed in Step 7 Basic 10.5? If you actually figured it out, perhaps sample pseudo-code would help. I need to do this quite often, so perhaps there is some magic in configuring the FB/FC to allow it to access memory directly rather than via the tag associated with a memory location. I'm new to Siemens PLCs, but have been programming PLCs for around 20 years. I miss the absolute control of Modicon, UDTs of A-B, and simplicity of Honeywell (yeah...). S7-1200 programming is potentially quite fabulous, but I cannot wait for v11 tobe released .. haveto get this project running now.
	science guy
Suggestion To thank Quote Answer

8/2/2010 10:29 AM	Rate (0)
Robster Gold Expert Joined: 5/28/2008 Last visit: 10/23/2024 Posts: 1343 Rating: (141)	Hi, you can use FieldRead and FieldWrite instructions. With FieldRead you can read char by char from your array and with FieldWrite you can fill up your string also char by char. With Label and Jump instruction you can build up the loop to read/write x-times. How do you program the "FieldRead" and "FieldWrite" instructions in STEP 7 Basic V10.5? Hope it hels regards

Suggestion To thank Quote Answer

8/2/2010 2:32 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/23/2024 Posts: 15531 Rating: (2462)	Ok, so now I can pick off the character elements one at a time. The fieldwrite only works with array elements, so a string output is no good. Guess I'll index through the input character stream, and concatenate to my output string until I run out of characters. That should work, at least in theory. Thanks.
	science guy
Suggestion To thank Quote Answer

8/2/2010 2:54 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/23/2024 Posts: 15531 Rating: (2462)	Ok, I tried, but no matter what I do, the strict type checking stops the process mid-way. I need to index through a string array as if it were a character array. I cannot find a way to do this. How about something like this.. is it possible and if so, what would the ladder look like?.. range(#msgLen_in,1,255)? return if not concat('', '', #String_out) add(1,0,->#counter) ----Loop---- FieldRead(#counter, fromCharArray1to20[1], toOutputArray[1]) concat(#String_out, toOutputArray[1]) add(1,0,->#counter) #counter<= #msgLen_in JMP(Loop) return #String_out I cannot get past the type checking or haven't figured out the tricky syntax that magically allows the software to ignore type and use memory addresses instead. Thanks for any suggestions.
	science guy
Suggestion To thank Quote Answer

8/9/2010 10:34 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/23/2024 Posts: 15531 Rating: (2462)	Bump -- I am still unable to get this to work even with field read/write. FieldWrite requires an array so it does not allow a string. Can I define a string and an array to point to the same memory? That would be nice.
	science guy
Suggestion To thank Quote Answer

8/10/2010 12:52 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 1/13/2025 Posts: 4391 Rating: (1462)	Hi, you can copy the contendes of a string to a char array variables first, and after that use field read/ write or check the string byte a byte (with many user code ...)
	Denilson Pegaia Siemens Industry Sector Technical Support
Suggestion To thank Quote Answer

8/10/2010 2:30 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/23/2024 Posts: 15531 Rating: (2462)	The comment about much user code is the only solution at this point... Sadly, the RS485 module places ASCII data into a CHAR array of a given length. I want to search for a string within the results, and to do that, I need a string. Sadly none of the supplied S7-1200 string commands function with a character array. What is normallyvery simple (inmany other PLCs) has become quite cumbersome and complicated. If there are some nice library functions or was to create a function that allows direct memory access, or to temporarily disable type checking, or ways to trick a block into accessing the memory regardless of type, please pass that along as it would simplify this problem.
	science guy
Suggestion To thank Quote Answer

8/10/2010 5:38 PM	Rate (1)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/23/2024 Posts: 15531 Rating: (2462)	Solved! In essence my earlier pseudo-code worked in combination with a FieldRead to index through the char array in a loop structure with successive String[1] concatenations. range(#in_chrLen,1,20)? return if not {my max conversion is 20) ' Initialize internal string to null / empty string concat('', '', #strScratch) MOVE(1,->#counter) ----Loop---- FieldRead{CHAR mode}(#counter, #in_ChrArray1to20[1], #chrScratch) ' use my CHR2STR function (see in another thread on how I implemented that) CHR2STR(#chrScratch,Global_DB.strScratch1) concat(Global_DB.strScratch1, #out_String) ' increment index add(1,#counter,->#counter) ' check to see if we're done #counter<= #in_chrLen JMP(Loop) if LEN(#out_String == #in_chrLen) RETurn TRUE otherwise RETurn FALSE This has been tested and works with variable number of input characters from 1 to 5 using a simple timer / counter event that sends varying input character arrays and displays the returned string on an HMI. Thanks to all those who made suggestions, asked questions, posted comments, etc. as they all helped come up with a solution that finally worked.
	science guy
Suggestion To thank Quote Answer
This contribution was helpful to 2 thankful Users O_Moderator MicroMan

|

Share this page:

Share this page on...

Follow us on