C++ regex replace whole word - c++

Question

I have a small game to do in which I need to sometimes replace some group of characters with the name of the player in the sentences.
For example, I could have a sentence like :
"[Player]! Are you okay? A plane crash happened, it's on fire!"
And I need to replace the "[Player]" with some name contained in a std::string.
I have been looking for about 20 minutes in other SO questions and in the CPP reference and I really can't understand how to use the regex.
I would like to know how I can replace all instances of the "[Player]" string in a std::string.

Answer 1

Personally I would not use regex for this. A simple search and replace should be enough.
These are (roughly) the functions I use:
// change the string in-place
std::string& replace_all_mute(std::string& s,
const std::string& from, const std::string& to)
{
if(!from.empty())
for(std::size_t pos = 0; (pos = s.find(from, pos) + 1); pos += to.size())
s.replace(--pos, from.size(), to);
return s;
}
// return a copy of the string
std::string replace_all_copy(std::string s,
const std::string& from, const std::string& to)
{
return replace_all_mute(s, from, to);
}
int main()
{
std::string s = "[Player]! Are you okay? A plane crash happened, it's on fire!";
replace_all_mute(s, "[Player]", "Uncle Bob");
std::cout << s << '\n';
}
Output:
Uncle Bob! Are you okay? A plane crash happened, it's on fire!

Answer 2

Regex is meant for more complex patterns. Consider, for example, that instead of simply matching [Player], you wanted to match anything between brackets. That would be a good use for regex.
Following is an example that does just that. Unfortunately, the interface of <regex> is not flexible enough to enable dynamic replacements, so we have to implement the actual replacing ourselves.
#include <iostream>
#include <regex>
int main() {
// Anything stored here can be replaced in the string.
std::map<std::string, std::string> vars {
{"Player1", "Bill"},
{"Player2", "Ted"}
};
// Matches anything between brackets.
std::regex r(R"(\[([^\]]+?)\])");
std::string str = "[Player1], [Player1]! Are you okay? [Player2] said that a plane crash happened!";
// We need to keep track of where we are, or else we would need to search from the start of
// the string everytime, which is very wasteful.
// std::regex_iterator won't help, because the replacement may be smaller
// than the match, and it would cause strings like "[Player1][Player1]" to not match properly.
auto pos=str.cbegin();
do {
// First, we try to get a match. If there's no more matches, exit.
std::smatch m;
regex_search(pos, str.cend(), m, r);
if (m.empty()) break;
// The interface of std::match_results is terrible. Let's get what we need and
// place it in apropriately named variables.
auto var_name = m[1].str();
auto start = m[0].first;
auto end = m[0].second;
auto value = vars[var_name];
// This does the actual replacement
str.replace(start, end, value);
// We update our position. The new search will start right at the end of the replacement.
pos = m[0].first + value.size();
} while(true);
std::cout << str;
}
Output:
Bill, Bill! Are you okay? Ted said that a plane crash happened!
See it live on Coliru

Answer 3

Simply find and replace, e.g. boost::replace_all()
#include <boost/algorithm/string.hpp>
std::string target(""[Player]! Are you okay? A plane crash happened, it's on fire!"");
boost::replace_all(target, "[Player]", "NiNite");

Answer 4

As some people have mentioned, find and replace might be more useful for this scenario, you could do something like this.
std::string name = "Bill";
std::string strToFind = "[Player]";
std::string str = "[Player]! Are you okay? A plane crash happened, it's on fire!";
str.replace(str.find(strToFind), strToFind.length(), name);