regex_replace multipe occurence

Question

I have the following code which works:

	std::wstring data = std::regex_replace(str, std::wregex(L"a"), L"+");
	data = std::regex_replace(data, std::wregex(L"b"), L"*");

Is there possible to replace those two chars at once, with a single regex_replace call ?

Answer 1

If you are interested in a single scan of input string, then try one of approaches:

using namespace std;

wregex regex( L"(a)|(b)|$" );

wcregex_iterator results_begin( str.c_str( ), str.c_str( ) + str.length( ), regex );
wcregex_iterator results_end{};

wstring data;

for( auto i = results_begin; i != results_end; ++i )
{
    const wcmatch& match = *i;

    data += match.prefix( ).str() + ( match[1].matched ? L"+" : match[2].matched ? L"*" : L"" );
}

or

for( auto i = results_begin; i != results_end; ++i )
{
    const wcmatch& match = *i;

    if( match[1].matched ) data += match.format( L"$`+" );
    else if( match[2].matched ) data += match.format( L"$`*" );
}

It is also possible to use for_each or transform.

Answer 2

Hi，
Currently, std::regex_replace does not support lambda like C#. It's hard to achieve what you want.

C#:

        string modifiedStr = Regex.Replace(str, "[ab]", match => {
            if (match.Value == "a")
            {
                return "+";
            }
            else if (match.Value == "b")
            {
                return "*";
            }
            return match.Value;
        });

Best regards,

Minxin Yu

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