[llvm-bugs] [Bug 51867] New: std::basic_ostream::seekp() > 2GiB

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51867

            Bug ID: 51867
           Summary: std::basic_ostream::seekp() > 2GiB
           Product: libc++
           Version: 12.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: davidwe at posteo.de
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

When I use the CLANG64 environment, the "seekp()" function does not work
correctly.

Everything > 2147483648 bytes ( 2 GiB ) ends in an "ios_base::clear:
unspecified iostream_category error" exception.

When I compile the example with "-D_FILE_OFFSET_BITS=64", the seekp() function
works as expected.

As an example:

#include <filesystem>
#include <fstream>
#include <iostream>
#include <stdio.h>

#define MAX_FILE_SIZE_3GiB 3221225472
#define MAX_FILE_SIZE_2GiB 2147483648

int main(int argc, char** argv)
{
    try {
        std::filesystem::path sourceFile =
std::filesystem::temp_directory_path() / "example_3GiB.bin";

        std::ofstream ofs(sourceFile);
        ofs << "this is some text in the new file\n";
        ofs.close();

        std::filesystem::resize_file(sourceFile, MAX_FILE_SIZE_3GiB);

        std::fstream file(sourceFile);
        file.exceptions(std::ifstream::failbit | std::ifstream::badbit);

        std::cout << "File size:  " << std::filesystem::file_size(sourceFile)
<< '\n';

        // One byte less works.
        file.seekp(MAX_FILE_SIZE_2GiB - 1, std::ios_base::beg);
        std::cout << "File tellp(): " << file.tellp() << '\n';

        // Everything larger than 2 GiB ends in an exception
        file.seekp(MAX_FILE_SIZE_2GiB + 1, std::ios_base::beg);
        std::cout << "File tellp(): " << file.tellp() << '\n';

        file.close();
        std::filesystem::remove(sourceFile);
        return 0;
    } catch(std::fstream::failure const& ex) {
        std::cout << ex.what() << '\n';
        return 0;
    } catch(std::filesystem::filesystem_error const& ex) {
        std::cout << ex.what() << '\n';
        return 0;
    }
}


Output:

    File size: 3221225472
    File tellp(): 2147483647
    ios_base::clear: unspecified iostream_category error

clang -v:

    clang version 12.0.1
    Target: x86_64-w64-windows-gnu
    Thread model: posix
    InstalledDir: C:/msys64/clang64/bin


A discussion is already going on in github. (
https://github.com/msys2/MINGW-packages/issues/9585 )

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