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std::fstream still good after closing and updating content #37400

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llvmbot opened this issue Jul 4, 2018 · 3 comments
Closed

std::fstream still good after closing and updating content #37400

llvmbot opened this issue Jul 4, 2018 · 3 comments
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bugzilla Issues migrated from bugzilla libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi.

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@llvmbot
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llvmbot commented Jul 4, 2018

Bugzilla Link 38052
Resolution FIXED
Resolved on Jan 07, 2019 18:50
Version unspecified
OS All
Reporter LLVM Bugzilla Contributor
CC @mclow

Extended Description

I have a simple program that should show the problem. - with libc++ the stream is still good after closing and further operation. Since also the file content was not updated - at least the stream operation fails on the closed stream and should set either failbit or badbit to reflect the situation.

#include
#include

int main(int argc, const char * argv[])
{
std::fstream ofs("test.txt", std::ios::out | std::ios::trunc);
ofs << "Hello, World!\n";
ofs.close();
ofs << "Hello, World!\n";
std::cout << "good(): " << ofs.good()
<< " fail(): " << ofs.fail()
<< " bad(): " << ofs.bad()
<< " eof(): " << ofs.eof() << std::endl;
return 0;
}

// http://coliru.stacked-crooked.com/a/cfaeb32849c9cfad

With libc++ I get
good(): 1 fail(): 0 bad(): 0 eof(): 0

Expected (or with libstdc++):
good(): 0 fail(): 1 bad(): 1 eof(): 0

I have tested on OSX with Xcode 9.4.1
Apple LLVM version 9.1.0 (clang-902.0.39.2)

or on Linux:
clang version 3.8.0

@llvmbot
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llvmbot commented Jul 4, 2018

assigned to @mclow

@mclow
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mclow commented Jul 31, 2018

This is https://stackoverflow.com/questions/51137052/libc-why-is-the-stream-still-good-after-closing (which I think you wrote, too)

The answer I gave there is still correct.

The standard says nothing about doing things to an fstream after calling close - so libc++'s behavior here is not "non-standard".
However, it is definitely surprising.

I have a patch that makes libc++ act like libstdc++, but I'm still looking into this.

Index: include/fstream

--- include/fstream (revision 338379)
+++ include/fstream (working copy)
@@ -702,6 +702,7 @@
_file = 0;
else
__rt = 0;

  • setbuf(0, 0);
    }
    return __rt;
    }

@mclow
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mclow commented Jan 8, 2019

Committed r350603 to resolve this.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 10, 2021
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Labels
bugzilla Issues migrated from bugzilla libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi.
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