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libstdc++: Implement P3223R2 Making std::istream::ignore less surprising 

libstdc++-v3/ChangeLog:

	* include/std/istream (ignore): Add an overload for char.
	* testsuite/27_io/basic_istream/ignore/char/93672.cc: Adjust
	expected behaviour for C++26 mode.
	* testsuite/27_io/basic_istream/ignore/char/4.cc: New test.

Co-authored-by: Jonathan Wakely <jwakely@redhat.com>
This commit is contained in:
Yuao Ma 2025-11-02 15:39:38 +08:00 committed by Jonathan Wakely
parent 01b8c6ffbd
commit 0d4ab66aaf
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3 changed files with 37 additions and 5 deletions
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12
libstdc++-v3/include/std/istream
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@ -42,6 +42,10 @@
#include <ios>
#include <ostream>
#if __cplusplus > 202302L
#include <concepts>
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
@ -537,7 +541,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* is extracted); note that this condition will never occur if
* @a __delim equals @c traits::eof().
*
* NB: Provide three overloads, instead of the single function
* NB: Provide four overloads, instead of the single function
* (with defaults) mandated by the Standard: this leads to a
* better performing implementation, while still conforming to
* the Standard.
@ -551,6 +555,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__istream_type&
ignore();
#if __cplusplus > 202302L
__istream_type&
ignore(streamsize __n, char __delim) requires same_as<_CharT, char>
{ return ignore(__n, traits_type::to_int_type(__delim)); }
#endif
/**
* @brief Looking ahead in the stream
* @return The next character, or eof().

22
libstdc++-v3/testsuite/27_io/basic_istream/ignore/char/4.cc Normal file
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@ -0,0 +1,22 @@
// { dg-do run { target c++26 } }
#include <istream>
#include <sstream>
#include <string>
#include <testsuite_hooks.h>
void test01() {
std::istringstream in("\xF0\x9F\xA4\xA1 Clown Face");
in.ignore(100, '\xA1');
VERIFY(in.gcount() == 4);
VERIFY(in.peek() == ' ');
std::string str;
in >> str;
VERIFY(str == "Clown");
}
int main() {
test01();
return 0;
}

8
libstdc++-v3/testsuite/27_io/basic_istream/ignore/char/93672.cc
View File

@ -20,9 +20,9 @@ test_pr93672() // std::basic_istream::ignore hangs if delim MSB is set
VERIFY( in.gcount() == 3 );
VERIFY( ! in.eof() );
// This only works if char is unsigned.
// Prior to C++26 (P3223R2), this only works if char is unsigned.
in.ignore(100, '\xfe');
if (std::numeric_limits<char>::is_signed)
if (std::numeric_limits<char>::is_signed && __cplusplus <= 202302L)
{
// When char is signed, '\xfe' != traits_type::to_int_type('\xfe')
// so the delimiter does not match the character in the input sequence,
@ -69,9 +69,9 @@ test_primary_template()
VERIFY( in.gcount() == 3 );
VERIFY( ! in.eof() );
// This only works if char is unsigned.
// Prior to C++26 (P3223R2), this only works if char is unsigned.
in.ignore(100, '\xfe');
if (std::numeric_limits<char>::is_signed)
if (std::numeric_limits<char>::is_signed && __cplusplus <= 202302L)
{
// When char is signed, '\xfe' != traits_type::to_int_type('\xfe')
// so the delimiter does not match the character in the input sequence,