[libcxx-commits] [libcxx] [libc++][istream] P3223R2: Making `std::istream::ignore` less surprising (PR #147007)

[Hristo Hristov via libcxx-commits]

================
@@ -0,0 +1,41 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// Requires 396145d in the built library.
+// XFAIL: using-built-library-before-llvm-9
+// XFAIL: FROZEN-CXX03-HEADERS-FIXME
+
+// <istream>
+
+// basic_istream& ignore(streamsize n, char_type delim);
+
+#include <cassert>
+#include <sstream>
+#include <string>
+
+#include "test_macros.h"
+
+int main(int, char**) {
+  std::istringstream in("\xF0\x9F\xA4\xA1 Clown Face");
+  in.ignore(100, '\xA1'); // ignore up to '\xA1' delimiter,
+                          // previously might have ignored to EOF
+
+  assert(in.gcount() == 4); // 4 bytes were ignored
+  assert(in.peek() == ' '); // next character is a space
+
+  std::string str; // read the next word
+  in >> str;
+  assert(str == "Clown");
+
+  // Parameter value "-1L" doesn't cause ambiguity with the char_type overload.
+  in.ignore(100, -1L); // ignore up to EOF, which is the default behavior
+  assert(in.eof());    // stream should be at EOF now
+  assert(in.gcount() == 5);
----------------
H-G-Hristov wrote:

```suggestion
  in.ignore(100, '\xA1'); // Ignore up to '\xA1' delimiter,
                          // previously might have ignored to EOF.

  assert(in.gcount() == 4); // 4 bytes were ignored.
  assert(in.peek() == ' '); // Next character is a space.

  std::string str; // Read the next word.
  in >> str;
  assert(str == "Clown");

  // Parameter value "-1L" doesn't cause ambiguity with the char_type overload.
  in.ignore(100, -1L); // Ignore up to EOF, which is the default behavior.
  assert(in.eof());    // Stream should be at EOF now.
  assert(in.gcount() == 5);
```

https://github.com/llvm/llvm-project/pull/147007