why can't i replace char on a string like this? - c++

Question

I'm trying to replace characters from the following map: const map<char, vector<char>> ass, note I have this string pasand I want to replace all (map value) vector chars to the Corresponding map key, I tried to iterate the map with a for cycle like this: (I got this code from another question on stackoverflow)
for (auto const &ent1 : ass) {
//ent1.first = first key
//ent1.second = second key
}
So I tried to iterate the map value vector like this:
string char1;
string char2;
string wr;
for (auto const &ent1 : ass) {
for (int i = 0; i < ent1.second.size(); i++) {
specialValues += ent1.second[i];
char2 = ent1.second[i];
char1 = ent1.first;
regex e("([" + char1 + "])");
cout << ("([" + char1 + "])");
cout << char2;
wr = regex_replace("c1a0", e, char2);
}
}
So I want the string "c1a0" to become "ciao" after the loops, but it just doesn't change anything,
I also tried:
wr = regex_replace("c1a0", e, "o");
output : c1a0
regex e("([0])");
wr = regex_replace("c1a0", e, char2);
output : c1a2
I don't know, it makes no sense for me. I don't understand, can you help me figure out what's wrong in my code?
Of course if I write:
regex e("([0])");
wr = regex_replace("c1a0", e, "o");
It gives me "c1ao" that's what I want.

Answer 1

Following code works for me:
#include <string>
#include <map>
#include <regex>
#include <iostream>
using namespace std;
int main() {
const map<char, vector<char>> ass = {
{ '1', {'i'} },
{ '0', {'o'} },
};
string char1;
string char2;
string wr = "c1a0";
for (auto const &ent1 : ass) {
for (int i = 0; i < ent1.second.size(); i++) {
//specialValues += ent1.second[i];
char2 = ent1.second[i];
char1 = ent1.first;
regex e("([" + char1 + "])");
cout << ("([" + char1 + "])") << std::endl;
cout << char2<< std::endl;
wr = regex_replace(wr, e, char2);
cout << wr << std::endl;
}
}
}
But IMHO, regex here is overkill. You can iterate over string manually and replace character like in the following snippet:
#include <string>
#include <set>
#include <iostream>
#include <vector>
using namespace std;
struct replace_entry {
char with;
std::set<char> what;
};
int main() {
const std::vector<replace_entry> replaceTable = {
{ 'i', {'1'} },
{ 'o', {'0'} },
};
string input = "c1a0";
for (auto const &replaceItem : replaceTable) {
for (char& c: input ) {
if(replaceItem.what.end() != replaceItem.what.find(c)) {
c = replaceItem.with;
}
}
}
cout << input << std::endl;
}
Yet another approach is to create 256 elements array of chars
#include <string>
#include <iostream>
class ReplaceTable {
private:
char replaceTable_[256];
public:
constexpr ReplaceTable() noexcept
: replaceTable_()
{
replaceTable_['0'] = 'o';
replaceTable_['1'] = 'i';
}
constexpr char operator[](char what) const noexcept {
return replaceTable_[what];
}
};
// One time initialization
ReplaceTable g_ReplaceTable;
int main() {
std::string input = "c1a0";
// Main loop
for (char& c: input ) {
if(0 != g_ReplaceTable[c] ) c = g_ReplaceTable[c];
}
std::cout << input << std::endl;
}