C ++ regex_match doesn't work
Here is part of my code
bool CSettings::bParseLine ( const char* input )
{
//_asm INT 3
std::string line ( input );
std::size_t position = std::string::npos, comment;
regex cvarPattern ( "\\.([a-zA-Z_]+)" );
regex parentPattern ( "^([a-zA-Z0-9_]+)\\." );
regex cvarValue ( "\\.[a-zA-Z0-9_]+[ ]*=[ ]*(\\d+\\.*\\d*)" );
std::cmatch matchedParent, matchedCvar;
if ( line.empty ( ) )
return false;
if ( !std::regex_match ( line.c_str ( ), matchedParent, parentPattern ) )
return false;
if ( !std::regex_match ( line.c_str ( ), matchedCvar, cvarPattern ) )
return false;
...
}
I am trying to split with it the lines I read from the lines of the file that look like this:
foo.bar = 15
baz.asd = 13
ddd.dgh = 66
and I want to extract parts from it - for example. for 1st line foo.bar = 15, I want to get something like:
a = foo
b = bar
c = 15
but now the regex always returns false, i tested it on many online riggers and even visual studio and it works fine, i need some other syntax for c ++ regex_match? I am using visual studio 2013 community
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The problem is that std :: regex_match must match the entire string, but you are trying to match only part of it.
You need to either use std :: regex_search or change your regex to match all three parts at the same time:
#include <regex>
#include <string>
#include <iostream>
const auto test =
{
"foo.bar = 15"
, "baz.asd = 13"
, "ddd.dgh = 66"
};
int main()
{
const std::regex r(R"~(([^.]+)\.([^\s]+)[^0-9]+(\d+))~");
// ( 1 ) ( 2 ) ( 3 ) <- capture groups
std::cmatch m;
for(const auto& line: test)
{
if(std::regex_match(line, m, r))
{
// m.str(0) is the entire matched string
// m.str(1) is the 1st capture group
// etc...
std::cout << "a = " << m.str(1) << '\n';
std::cout << "b = " << m.str(2) << '\n';
std::cout << "c = " << m.str(3) << '\n';
std::cout << '\n';
}
}
}
Regular expression: https://regex101.com/r/kB2cX3/2
Output:
a = foo
b = bar
c = 15
a = baz
b = asd
c = 13
a = ddd
b = dgh
c = 66
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To focus on templates regex
, I would rather use raw string literals in C ++:
regex cvarPattern ( R"rgx(\.([a-zA-Z_]+))rgx" );
regex parentPattern ( R"rgx(^([a-zA-Z0-9_]+)\.)rgx" );
regex cvarValue ( R"rgx(\.[a-zA-Z0-9_]+[ ]*=[ ]*(\d+\.*\d*))rgx" );
Everything between the delimiters rgx(
)rgx
does not need additional escaping for C ++ char characters.
Actually what you wrote in your question is similar to those regexes I wrote as string literals.
You probably just meant something like
regex cvarPattern ( R"rgx(.([a-zA-Z_]+))rgx" );
regex parentPattern ( R"rgx(^([a-zA-Z0-9_]+).)rgx" );
regex cvarValue ( R"rgx(.[a-zA-Z0-9_]+[ ]*=[ ]*(\d+(\.\d*)?))rgx" );
I didn't dig deeper, but now I am not getting all those escaped characters in your regex patterns.
Regarding your question in the comment, you can use a selection of suitable submatrix groups and check which one was applied in the match structure:
regex cvarValue (
R"rgx(.[a-zA-Z0-9_]+[ ]*=[ ]*((\d+)|(\d+\.\d?)|([a-zA-Z]+)){1})rgx" );
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
You probably do not need these regular expressions cvarPattern
and parentPattern
to check for other (more detailed) ideas about the appropriate template.
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