How to delete plain "\n" from a string in C++?

Question

As above, I'm trying to delete two character sub-string (not new-line character, just plain text) from a line.

What I am doing right now is line.replace(line.find("\\n"), 3, ""); because I wanted to escape it, but I receive debug error saying that abort() has been called. Moreover, I am not sure about size 3, because first slash shouldn't be treated as a literal character.

Please create a [mcve]. I am sure you have a typo on line 23, but still you better show us the code — 463035818_is_not_an_ai, Sep 11 '18 at 09:50
You want to remove two characters ('\' and 'n'), not three. You also need to check that the string was found. — molbdnilo, Sep 11 '18 at 09:55
https://stackoverflow.com/questions/32435003/how-to-remove-all-substrings-from-a-string — hellow, Sep 11 '18 at 09:56
Have you tried raw string literal? Maybe those don't escape? R"(\\n)" — huseyin tugrul buyukisik, Sep 11 '18 at 09:56
I rather would use `std::regex_replace(line, "(\\n)+", "");` And your code doesn't account for case that you won't find the match. Or fact that you remove 3 characters instead of two. — Swift - Friday Pie, Sep 11 '18 at 10:09
@Swift-FridayPie Why would someone use regex to delete constant? — Zereges, Sep 11 '18 at 10:13
@Zergeres Pros: clean one-liner, replaces all occurrences, got option to construct new string or write to existing one (if iterator syntax used), if required pattern changes to something else and can overlap, it would still work. Cons: performance, just what you said, to replace only one occurrence needs some magic. — Swift - Friday Pie, Sep 11 '18 at 13:13
@LightnessRacesinOrbit got me there.. that's what happens when I post from phone. Four backslashes, of course, regex needs its escaping too. Also you don't want to know what SwiftKey tried to suggest instead of code. — Swift - Friday Pie, Sep 11 '18 at 13:19
@Swift-FridayPie I was [joking](https://blog.codinghorror.com/regular-expressions-now-you-have-two-problems/) :P — Lightness Races in Orbit, Sep 11 '18 at 13:58
@LightnessRacesinOrbit But it was appropriate. Regex uses \ in samilar way to C\C++. — Swift - Friday Pie, Sep 11 '18 at 17:47
@Swift-FridayPie Actually that's a good point and I hadn't even thought about that. Hah! — Lightness Races in Orbit, Sep 11 '18 at 17:47
@Swift-FridayPie Do I get to hear SwiftKey's suggestion now, as a reward? ;) — Lightness Races in Orbit, Sep 11 '18 at 17:48

Petr Mánek · Accepted Answer · 2018-09-11T10:10:44.653

2

I guess this is exactly what you're looking for:

std::string str = "This is \\n a string \\n containing \\n a lot of \\n stuff.";
const std::string to_erase = "\\n";

// Search for the substring in string
std::size_t pos = str.find(to_erase);
while (pos != std::string::npos) {
    // If found then erase it from string
    str.erase(pos, to_erase.length());
    pos = str.find(to_erase);
}

Note that you're likely getting std::abort because you are passing std::string::npos or the length 3 (not 2) to std::string::replace.

edited Sep 11 '18 at 10:10

answered Sep 11 '18 at 09:59

Petr Mánek

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You are of course correct, I was typing in a haste. The code is operating as expected now, here you can see it in action: https://ideone.com/nHRc0k – Petr Mánek Sep 11 '18 at 10:11
This is exactly what I was looking for, thank you so much! – Radoslaw Dubiel Sep 12 '18 at 09:16

score 0 · Answer 2 · answered Sep 11 '18 at 11:20

#include <iostream>
#include <string>
int main()
{

std::string head = "Hi //nEveryone. //nLets //nsee //nif //nthis //nworks";
std::string sub = "//n";
std::string::iterator itr;
for (itr = head.begin (); itr != head.end (); itr++)
{
  std::size_t found = head.find (sub);
  if (found != std::string::npos)
head.replace (found, sub.length (), "");

}
 std::cout << "after everything = " << head << std::endl;
}

i got the output as :

after everything = Hi Everyone. Lets see if this works

All is good, but why / instead of \ ? That's the berry of this question. — Swift - Friday Pie, Sep 11 '18 at 13:14

How to delete plain "\n" from a string in C++?

2 Answers2