RegexReplace different output according to compiler

Question

#include <iostream>
#include <regex>

int main()
{
    std::string text = R"(11111111111111111111
11111111111111111111
11111111111111111111
11111111111110000000
11111111111000000000
11111111100011111100
11111111100111100000)";

    std::regex re("^1+\n");
    std::string str = std::regex_replace(text, re, "");
    std::cout << str;
  return 0;
}

Why does the exact same code when compiled under visual studio, trims all lines containing 11111111111111111111?

I would like to it behave the same as on the link above, replacing just the first occurrence.

Do i need any kind of 'special' flag into the regex?

In MSVC, the `^` anchor matches start of any line, not just the start of a string. — Wiktor Stribiżew, Sep 07 '22 at 07:41
@WiktorStribiżew how do i 'tell' it to match just the first line? — Cesar, Sep 07 '22 at 19:55

score 1 · Accepted Answer · answered Sep 07 '22 at 02:58

1

I modified my answer. It might be a compiler difference. You can refer to the flags and similar thread.

std::regex_constants::match_flag_type fonly =
    std::regex_constants::format_first_only;
std::regex re("^1+\n");
std::string str = std::regex_replace(text, re, "", fonly);

answered Sep 07 '22 at 02:58

Minxin Yu - MSFT

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When should i use this flag? – Cesar Sep 07 '22 at 03:01
So can i assume that this flag set `regex_replace` to replace only the `first` occurence?https://stackoverflow.com/questions/33105581/stdregex-replace-only-first-occurence – Cesar Sep 07 '22 at 03:19
To begin, why does the regex match things in multiple lines? By default std::regex lib matches things multi-line? – Cesar Sep 07 '22 at 03:40
[MSDN document](https://learn.microsoft.com/en-us/cpp/standard-library/regex-constants-class?view=msvc-170#match_flag_type)`format_first_only -- do not search for matches after the first one.` . Looks like regex matches multiple lines by default. – Minxin Yu - MSFT Sep 07 '22 at 05:25
E.g. The description of the document `regex_match`: Tests whether a regular expression matches the **entire target string**. – Minxin Yu - MSFT Sep 07 '22 at 05:34

RegexReplace different output according to compiler

1 Answers1