[Bug libstdc++/94749] New: std::istream::ignore discards too many characters

[serpent7776 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94749

            Bug ID: 94749
           Summary: std::istream::ignore discards too many characters
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: serpent7776 at gmail dot com
  Target Milestone: ---

Created attachment 48369
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48369&action=edit
full source example

The following code results in '=' assigned to c when using libstdc++, but '+'
is assigned when using libc++, I believe libc++ is correct here

        std::stringstream s(" +=");
        char c;
        s.ignore(1, '+');
        s >> c;

Tested this on godbolt with newest gcc and locally on FreeBSD with gcc7
(command: g++7 -Wall -Wextra -pedantic test.cpp)

https://godbolt.org/z/yS5je8