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Fix compilation error on CentOS 7 (gcc 4.8)#22313

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opencv-pushbot merged 1 commit intoopencv:4.xfrom
mateusztabaka:getline
Aug 3, 2022
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Fix compilation error on CentOS 7 (gcc 4.8)#22313
opencv-pushbot merged 1 commit intoopencv:4.xfrom
mateusztabaka:getline

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@mateusztabaka mateusztabaka commented Jul 27, 2022

libstdc++ that comes with gcc 4.8 doesn't
define getline(basic_istream<char>&&, std::string&)
even if it's part of the c++11 standard.
However we can still use the following:
getline(basic_istream<char>&, std::string&).

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@mateusztabaka
Fix compilation error on CentOS 7 (gcc 4.8)
a898689 
libstdc++ that comes with gcc 4.8 doesn't
define `getline(basic_istream<char>&&, std::string&)`
even if it's part of the c++11 standard.
However we can still use the following:
`getline(basic_istream<char>&, std::string&)`.
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mateusztabaka commented Jul 28, 2022

@hzcyf what do you think?

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zihaomu commented Jul 28, 2022

Hi @mateusztabaka, thanks for your contribution!

I have a question about the code:
On my local computer (the compiler is llvm13), I found the

std::getline(std::ifstream(video + "/device/interface"), uvcDev.name);

was parsed as the getline(basic_istream<char>&, std::string&) instead of getline(basic_istream<char>&&, std::string&).

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hzcyf commented Jul 28, 2022

@hzcyf what do you think?

@mateusztabaka Thanks for your test and contribution！

I have tested this PR on ubuntu18.04 with GCC7.5， it‘s running well!
I think your modifications can improve the compatibility of our code. It should be merged.

Sorry for my bad English！

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mateusztabaka commented Jul 28, 2022

hi @zihaomu. That's interesting, I can see the same behavior that you mentioned with a simple snippet put into compiler explorer: https://gcc.godbolt.org/z/3fcEbaz5M. Also similar behavior I see for gcc >= 6.1. However with no optimizations getline(basic_istream<char>&&, std::string&) is used. Summary in the table below:

compiler/optimizationsgetline version usedlink to CE
clang 13.0.1 with -O3getline(basic_istream&, std::string&)https://gcc.godbolt.org/z/3fcEbaz5M
clang 13.0.1 with -O0getline(basic_istream&&, std::string&)https://gcc.godbolt.org/z/TeMrbohqx
gcc 12.1 with -O3getline(basic_istream&, std::string&)https://gcc.godbolt.org/z/EffabjYbs
gcc 12.1 with -O0getline(basic_istream&&, std::string&)https://gcc.godbolt.org/z/dxxErxhE8
gcc 4.8.5none, compilation errorhttps://gcc.godbolt.org/z/fWYEcGcM5

@asmorkalov asmorkalov requested a review from alalek July 28, 2022 10:20
zihaomu
zihaomu approved these changes Jul 28, 2022
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LGTM!👍
With this path, it can pass GCC 4.8 successfully.
Passed case: https://gcc.godbolt.org/z/KjbWc156b

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mateusztabaka commented Aug 1, 2022

Can this be merged or should we wait for someone else's approval (I can see that Alexander Alekhin is on vacation)?

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vpisarev commented Aug 3, 2022

@alalek, this fixes compile problems on CentOS, which is super-popular in some orgs. Can we merge it quickly?

@asmorkalov asmorkalov self-requested a review August 3, 2022 09:29
@asmorkalov asmorkalov self-assigned this Aug 3, 2022
@opencv-pushbot opencv-pushbot merged commit 8bfe620 into opencv:4.x Aug 3, 2022
@mateusztabaka mateusztabaka deleted the getline branch August 7, 2022 21:58
@alalek alalek mentioned this pull request Aug 21, 2022
Merged
@asmorkalov asmorkalov added this to the 4.7.0 milestone Jan 23, 2023
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@asmorkalov asmorkalov asmorkalov approved these changes

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