How to get result from regexp_match() [duplicate] - c++

Question

This question already has an answer here:
no matching function for call to ‘regex_search(...)'
(1 answer)
Closed 3 years ago.
My code should do this:
input: (x+y) => (x*y)
output: (x+y)
regexp works well I tested them on a website regexp101.com
If I remove the match parameter from regexp_match() code works.
But it does not return the regexp result.
I get this error when I run this command:
> g++ -std=c++11 main.cpp
ERROR
main.cpp:14:9: error: no matching function for call to 'regex_match'
if (regex_match(formula,match, firstBrace)){
^~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/regex:6038:1: note:
candidate template ignored: deduced conflicting types for parameter '_BidirectionalIterator'
('std::__1::basic_string<char>' vs. 'std::__1::match_results<const char *,
std::__1::allocator<std::__1::sub_match<const char *> > >')
regex_match(_BidirectionalIterator __first, _BidirectionalIterator __last,
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/regex:6049:1: note:
candidate template ignored: could not match 'const _CharT *' against 'std::__1::string' (aka
'basic_string<char, char_traits<char>, allocator<char> >')
regex_match(const _CharT* __str, match_results<const _CharT*, _Allocator>& __m,
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/regex:6059:1: note:
candidate template ignored: deduced type 'match_results<typename basic_string<char,
char_traits<char>, allocator<char> >::const_iterator, [...]>' of 2nd parameter does not match
adjusted type 'match_results<const char *, [...]>' of argument [with _ST =
std::__1::char_traits<char>, _SA = std::__1::allocator<char>, _Allocator =
std::__1::allocator<std::__1::sub_match<const char *> >, _CharT = char, _Traits =
std::__1::regex_traits<char>]
regex_match(const basic_string<_CharT, _ST, _SA>& __s,
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/regex:6080:1: note:
candidate template ignored: could not match 'const _CharT *' against 'std::__1::string' (aka
'basic_string<char, char_traits<char>, allocator<char> >')
regex_match(const _CharT* __str, const basic_regex<_CharT, _Traits>& __e,
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/regex:6089:1: note:
candidate template ignored: could not match 'basic_regex' against 'match_results'
regex_match(const basic_string<_CharT, _ST, _SA>& __s,
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/regex:5366:5: note:
candidate function template not viable: requires at least 4 arguments, but 3 were provided
regex_match(_Bp, _Bp, match_results<_Bp, _Ap>&, const basic_regex<_Cp, _Tp>&,
^
1 error generated.
#include <iostream>
#include <string>
#include <regex>
using namespace std;
int main() {
string formula;
cout << "Write down a formula" << endl;
cin >> formula;
cmatch match;
regex firstBrace("(\\()(\\w\\+)+(.\\))\\s?");
if (regex_match(formula,match, firstBrace)){
cout << "String 'a' matches regular expression 'b' \n";
cmatch mcopy (match); // copy constructor
for (unsigned i=0; i<mcopy.size(); ++i)
cout << "match " << i << ": " << mcopy[i] << endl;
}
return 0;
}
How can I get the result from regexp?

Answer 1

Your current code doesn't compile because type of target doesn't match to type of match results. If you pass string as input, matched results will be stored in smatch. When input is const char*, results are stored in cmatch.
You have to replace cmatch occurences by smatch.