https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102259
Bug ID: 102259
Summary: ifstream::read(…, count) fails when count >= 2^31 on
darwin
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: mimomorin at gmail dot com
Target Milestone: ---
Created attachment 51431
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51431&action=edit
Testcase for ifstream::read(…, count >= 2^31)
I tried to read a large file using `ifstream::read` on Mac, but it fails to
read any byte when count >= 2^31. Note that the system is 64-bit and
`std::streamsize` has 8 bytes.
Here is a testcase.
#include <iostream>
#include <fstream>
int main() {
std::ifstream is{"2GB.bin", std::ios::binary}; // filesize >= 2^31 bytes
auto buffer = new char[1LL << 31];
is.read(buffer, 1LL << 31);
std::cout << is.good() << " (" << is.gcount() << " bytes)\n";
// Expected output: "1 (2147483648 bytes)"
// Actual output (on Mac): "0 (0 bytes)"
}
My system is macOS 10.15 running on x86_64 Mac. The testcase failed on
Homebrew's GCC (ver. 6, 9, 10, 11) and MacPorts' GCC (ver. 6), but it succeeded
on LLVM Clang (trunk) and Apple Clang (ver. 12).
`ifstream::read(…, count)` works fine when count < 2^31. So if we split
is.read(buffer, 1LL << 31);
into
is.read(buffer, (1LL << 31) - 1);
is.read(buffer + (1LL << 31) - 1, 1);
then everything goes OK.
Additionally, `istringstream::read(…, count >= 2^31)` works fine both on GCC
and Clang.
I don't think this simple issue went unnoticed, so maybe I've missed something.
