removing a zero width character in c++?

Question

I'm working on a c++ file and I've encountered an interesting problem. I'm outputting strings into a text file (using ofstream) and I have the following lines.

void InstructionWriter::outputLabel(string s){
string sLabel;
sLabel = s;
sLabel.erase(remove(sLabel.begin(), sLabel.end(), ' '),sLabel.end());

sLabel = "(" + function + "$" + sLabel + ")\n" ;
outputFile << sLabel;
}

The problem is during the txt file it outputs.

When I head to the text file where outputLabel was run, highlighting the line counts the characters +1 character. that +1 is "invisible." Highlighting the line won't select it. The only way to fix it is to start deleting from the right. After you hit the ')' I'll notice that I hit delete again but the cursor didn't move and it seems like nothing got deleted.

I think It's sneaking in a zero width character but I don't know how to strip that from the string, does anybody have any ideas on what functions to look into?

@smac89

terminate called after throwing an instance of 'std::length_error'
  what():  basic_string::_M_replace
0

That is what the terminal threw at me after running that command you mentioned.

What is `function` ? Edit your question to include a [mcve]. — Sid S, Dec 06 '18 at 04:09
you should open with some binary editor to make sure that character really exist. — apple apple, Dec 06 '18 at 04:10
What is the input? What is the expected and actual output? How do you know that there's "+1 character"? — Some programmer dude, Dec 06 '18 at 04:10
@Someprogrammerdude I'm working on Project 8 for Nand2tetris. if you're familiar with that, I'm reading a vm file and outputting it's equivalent hack instruction. This hack instruction is for printing labels to the text file. — Dart Feld, Dec 06 '18 at 04:14
@SidS function is a string being pulled in from the global space. I'll edit my question a bit more to help specify the issue. — Dart Feld, Dec 06 '18 at 04:14
Instead of writing the output to a fie, write to `std::cout`, then run your program like this: `./myprog | tee /dev/stderr | wc -c`. What output do you get? Paste the output of the command in your question — smac89, Dec 06 '18 at 04:16

Ali Tavakol · Answer 1 · 2018-12-06T04:40:15.083

0

Instead of sLabel.erase(remove(sLabel.begin(), sLabel.end(), ' '),sLabel.end()); please try this:

std::string from = " ", to = "";
size_t start_pos = 0;
while ((start_pos = sLabel.find(from, start_pos)) != std::string::npos) {
  sLabel.replace(start_pos, from.length(), to);
  start_pos += to.length();
}

Because the string is UTF-8 encoded; and You cannot rely on individual bytes. Manipulate sub-strings only.

edited Dec 06 '18 at 04:40

answered Dec 06 '18 at 04:19

Ali Tavakol

405
3
11

If you can use boost, there is a compact solution: `boost::replace_all(sLabel, " ", "");` – Ali Tavakol Dec 06 '18 at 04:41

score 0 · Answer 2 · answered Dec 06 '18 at 04:37

0

Everyone, I was able to figure it out.

per Smacs comment, I uploaded the output text file to a binary editor. oddly enough, I found an 0D before the newline character that I manually put in.

I used a regex replace on the string and now it's not adding that 0D character in the string.

Thanks for all the tips.

answered Dec 06 '18 at 04:37

Dart Feld

21
4

@Ali No it's not. There's no specified encoding in the C++ specification. Most likely it's ASCII encoded, as that's the usual encoding on most systems since a few decades. – Some programmer dude Dec 06 '18 at 04:50
Let me guess, you're on a Windows system? Then that's *normal* as the end-of-line sequence on Windows is `"\r\n"`. What you see is the carriage-return `'\r'`. And that's how text-files work, a newline is translated to the OS-specific end-of-line sequence when writing, and the opposite translation when reading. Don't remove it, unless you need to copy the file to a POSIX system (like Linux or macOS, and then there are utilities that can convert between the platforms). – Some programmer dude Dec 06 '18 at 04:52
So, if we have `std::string s = "سلام";` in Arabic, how do you think bytes will be? – Ali Tavakol Dec 06 '18 at 08:20

removing a zero width character in c++?

2 Answers2