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Fix over-writing library prologue #5244

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xbauch wants to merge 1 commit into from
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Fix over-writing library prologue #5244

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4 changes: 3 additions & 1 deletion src/ansi-c/cprover_library.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,9 @@ std::string get_cprover_library_text(
const struct cprover_library_entryt cprover_library[],
const std::string &prologue)
{
std::ostringstream library_text(prologue);
// the default mode is ios_base::out which means subsequent write to the
// stream will overwrite the original content
std::ostringstream library_text(prologue, std::ios_base::ate);
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@hannes-steffenhagen-diffblue hannes-steffenhagen-diffblue Feb 25, 2020 •
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#include <iostream>
#include <sstream>
int main(void) {
  std::ostringstream send_help{"SOS"};
  send_help << "WAT";
  std::cout << send_help.str() << '\n';
}

Try it online!

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@thk123 thk123 Feb 25, 2020

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WAT is the point of this constructor...
A potentially more obvious fix might be

std::ostringstream library_text;
library_text << prologue

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@hannes-steffenhagen-diffblue hannes-steffenhagen-diffblue Feb 25, 2020

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@thk123 In a slightly less humorous note, I can see uses for this (for example, if you need to guarantee some minimum width for the output so you add in a bunch of filler characters to override first), the “wtf” here is that this is the default, which I think few sane people would expect.

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@xbauch xbauch Feb 25, 2020

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std::ostringstream library_text(prologue);
library_text.seekp(0, library_text.end);

would also work.

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@chrisr-diffblue chrisr-diffblue Feb 25, 2020

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I'd personally lean either towards the solution @thk123 suggested, or to the original solution @xbauch had in the PR. I think the alternative using seekp just looks even more odd :-) Though I appreciate the oddness comes from the C++ spec here.


std::size_t count=0;

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