Replace N formulas to one (string interpolation)

Question

Is it possible in c++ to do such string conversion as:

Example:

From:

F = a && b && c;
H = p ^ 2 + w
K = H > 10 || e < 5;
J = F && !K;

To:

J = (a && b && c) && !( (p ^ 2 + w) > 10 || e < 5);

Yes, this is possible. If in doubt, consult the [operator precedence table](http://en.cppreference.com/w/cpp/language/operator_precedence). — Henri Menke, May 22 '17 at 00:14
@HenriMenke I mean to convert it from the first form to the other. I guess some kind of recursion is in place, maybe my question is not very clear and people started downvoting for that reason. — Anna K., May 22 '17 at 00:16
@AnnaK. The two code snippets are not equivalent by the way. https://godbolt.org/g/SrJwv8 — Henri Menke, May 22 '17 at 00:31
@AnnaK. That's not hard to notice. In my example `e`, `p`, and `w` are integers. Also that does not change the statement that the two lines are not equivalent, which is also why the compiler can *never* turn one into the other. — Henri Menke, May 22 '17 at 00:38

Jonathan Mee · Accepted Answer · 2017-05-22T17:09:04.417

3

It looks like you're asking for interpolation. In which case sure! First you'll want to construct a map<string, string> of the keys and values, for example:

map<string, string> interpolate = { { "F"s, "a && b && c"s }, { "H"s, "p ^ 2 + w"s }, { "K"s, "H > 10 || e < 5"s }, { "J"s, "F && !K"s } };

Then just use for_each, stding::find, and string::replace.

for(const auto& i : interpolate) for_each(begin(interpolate), end(interpolate), [&](auto& it){ for(auto pos = it.second.find(i.first); pos != string::npos; pos = it.second.find(i.first, pos)) it.second.replace(pos, i.first.size(), '(' + i.second + ')'); });

Live Example

After running this code, when outputting interpolate with for(const auto& i : interpolate) cout << i.first << " : " << i.second << endl You'll get:

F : a && b && c
H : p ^ 2 + w
J : (a && b && c) && !((p ^ 2 + w) > 10 || e < 5)
K : (p ^ 2 + w) > 10 || e < 5

edited May 22 '17 at 17:09

answered May 22 '17 at 01:31

Jonathan Mee

37,899
23
129
288

Not only you understood my question but you covered the theory behind this (and imparted us, those that do not how to name this type of problem, a little more wisdom) *and* you provided an example. People who down-voted this should take example from you Sir: first you read the question to understand what's being asked *then* you judge and possibly give a valid reason why you downvoted . Thank you so much for keeping this site bright like a diamond! – Anna K. May 22 '17 at 14:14
Also, what's the purpose of `s` after each string? – Anna K. May 22 '17 at 14:22
1

@AnnaK. That's the [`""s` operator](http://en.cppreference.com/w/cpp/string/basic_string/operator%22%22s). `"F"s` is equivalent to `string("F")`. – Jonathan Mee May 22 '17 at 14:31
Hi Jonathan, I think there is a minor flaw with a special case: what happens if we have a circle like: `J = J && F && !K;`? (live compiler seems to abort). – Anna K. Jun 09 '17 at 19:57
@AnnaK That would be an infinite loop, no matter how many times you interpolated J there would still be a J that needed to be interpolated. So no, my algorithm cannot output an infinitely repeating sequence, but since neither can anything else... I'm not gonna consider that a problem. – Jonathan Mee Jun 09 '17 at 21:16
I'm sorry I put it wrong maybe: what if instead of looping through infinite times, the moment it saw a cycle recursion, it stopped (for that particular variable analysis). – Anna K. Jun 09 '17 at 22:41
1

@AnnaK. You can do that with a conditional of course. But if you find you need help writing it, it's outside the scope of your original question, so you'll need to post a new question on that. If you post a link I'll gladly come take a stab at answering. – Jonathan Mee Jun 09 '17 at 23:51
I have a problem porting it to c++98: https://stackoverflow.com/questions/44637892/port-string-interpolation-from-c14-to-c98 – Anna K. Jun 19 '17 at 19:11

Replace N formulas to one (string interpolation)

1 Answers1

Linked