Revert fstream.seekp(0, ios::cur) change (#3841)

stl/inc/__msvc_filebuf.hpp

@@ -651,7 +651,8 @@ class basic_filebuf : public basic_streambuf<_Elem, _Traits> { // stream buffer
             _Off -= static_cast<off_type>(sizeof(_Elem)); // back up over _Elem bytes
         }
 
-        if (!_Myfile || !_Endwrite() || _CSTD _fseeki64(_Myfile, _Off, _Way) != 0
+        if (!_Myfile || !_Endwrite()
+            || ((_Off != 0 || _Way != ios_base::cur) && _CSTD _fseeki64(_Myfile, _Off, _Way) != 0)
             || _CSTD fgetpos(_Myfile, &_Fileposition) != 0) {
             return pos_type{off_type{-1}}; // report failure
         }

tests/std/test.lst

@@ -223,10 +223,10 @@ tests\GH_003022_substr_allocator
 tests\GH_003105_piecewise_densities
 tests\GH_003119_error_category_ctor
 tests\GH_003246_cmath_narrowing
-tests\GH_003572_fstream_seekp_0_cur
 tests\GH_003617_vectorized_meow_element
 tests\GH_003676_format_large_hh_mm_ss_values
 tests\GH_003735_char_traits_signatures
+tests\GH_003840_tellg_when_reading_lf_file_in_text_mode
 tests\LWG2381_num_get_floating_point
 tests\LWG2597_complex_branch_cut
 tests\LWG3018_shared_ptr_function

tests/std/tests/GH_003572_fstream_seekp_0_cur/env.lst → tests/std/tests/GH_003840_tellg_when_reading_lf_file_in_text_mode/env.lst

@@ -1,4 +1,4 @@
 # Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-RUNALL_INCLUDE ..\usual_matrix.lst
+RUNALL_INCLUDE ..\usual_17_matrix.lst

tests/std/tests/GH_003840_tellg_when_reading_lf_file_in_text_mode/test.cpp

@@ -0,0 +1,51 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <filesystem>
+#include <fstream>
+#include <ios>
+#include <string>
+
+#include "temp_file_name.hpp"
+
+using namespace std;
+
+void test(const string& temp_file_name_str, const ios_base::openmode mode) {
+    filesystem::remove(temp_file_name_str);
+
+    {
+        ofstream out{temp_file_name_str, mode};
+        out << "Line A\n";
+        out << "Line B\n";
+        out << "Line C\n";
+    }
+
+    {
+        ifstream in{temp_file_name_str};
+        string line;
+
+        assert(getline(in, line));
+        assert(line == "Line A");
+        (void) in.tellg();
+
+        assert(getline(in, line));
+        assert(line == "Line B");
+        (void) in.tellg();
+
+        assert(getline(in, line));
+        assert(line == "Line C");
+        (void) in.tellg();
+
+        assert(!getline(in, line));
+    }
+
+    filesystem::remove(temp_file_name_str);
+}
+
+int main() {
+    const string temp_file_name_str = temp_file_name();
+
+    test(temp_file_name_str, ios_base::out);
+    test(temp_file_name_str, ios_base::binary);
+}