Why does the `int` overload of `abs` get called in my code?
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I've had a super frustrating bug in my code for the past few weeks. My code would work exactly as expected on my computer, but as soon as I farmed it out to the HPC server, it would produce weird results.
I've boiled it down to this: on my computer (iMac) the function abs() works with floating point numbers, but on the server abs() truncates it to an integer.
Example:
Server
abs(-1.1341234) = 1
My Mac
abs(-1.1341234) = 1.1341234
Now I know I can fix this by using fabs(), that's not the question. I looked at the versions of gcc on either machine and this is the output:
Server
g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/apps/software/GCCcore/5.4.0/libexec/gcc/x86_64-unknown-linux-gnu/5.4.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --enable-languages=c,c++,fortran --enable-lto --enable-checking=release --disable-multilib --enable-shared=yes --enable-static=yes --enable-threads=posix --enable-gold=default --enable-plugins --enable-ld --with-plugin-ld=ld.gold --prefix=/apps/software/GCCcore/5.4.0 --with-local-prefix=/apps/software/GCCcore/5.4.0 --enable-bootstrap --with-isl=/dev/shm/GCCcore/5.4.0/dummy-/gcc-5.4.0/stage2_stuff
Thread model: posix
gcc version 5.4.0 (GCC)
My Mac
g++ -v
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/include/c++/4.2.1
Apple LLVM version 10.0.1 (clang-1001.0.46.3)
Target: x86_64-apple-darwin18.5.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
So my question, why does abs() produce different results between gcc and clang? This issue literally cost me 3 weeks of progress, so as you can imagine I'm a little salty just now...
c++ gcc compilation clang
edited 12 mins ago
J. Antonio Perez
3,533926
asked 1 hour ago
PhillPhill
21415
add a comment |
I've had a super frustrating bug in my code for the past few weeks. My code would work exactly as expected on my computer, but as soon as I farmed it out to the HPC server, it would produce weird results.
I've boiled it down to this: on my computer (iMac) the function abs() works with floating point numbers, but on the server abs() truncates it to an integer.
Example:
Server
abs(-1.1341234) = 1
My Mac
abs(-1.1341234) = 1.1341234
Now I know I can fix this by using fabs(), that's not the question. I looked at the versions of gcc on either machine and this is the output:
Server
g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/apps/software/GCCcore/5.4.0/libexec/gcc/x86_64-unknown-linux-gnu/5.4.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --enable-languages=c,c++,fortran --enable-lto --enable-checking=release --disable-multilib --enable-shared=yes --enable-static=yes --enable-threads=posix --enable-gold=default --enable-plugins --enable-ld --with-plugin-ld=ld.gold --prefix=/apps/software/GCCcore/5.4.0 --with-local-prefix=/apps/software/GCCcore/5.4.0 --enable-bootstrap --with-isl=/dev/shm/GCCcore/5.4.0/dummy-/gcc-5.4.0/stage2_stuff
Thread model: posix
gcc version 5.4.0 (GCC)
My Mac
g++ -v
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/include/c++/4.2.1
Apple LLVM version 10.0.1 (clang-1001.0.46.3)
Target: x86_64-apple-darwin18.5.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
So my question, why does abs() produce different results between gcc and clang? This issue literally cost me 3 weeks of progress, so as you can imagine I'm a little salty just now...
c++ gcc compilation clang
edited 12 mins ago
J. Antonio Perez
3,533926
asked 1 hour ago
PhillPhill
21415
3
so as you can imagine I'm a little salty just now... Annoying but worth the lecture... This will make you very sensitive about these things. ;-) (I don't mean this offensive but rather as a "heads up". Every really annoying bug might at least produce a valuable experience. So, take it positively...)
– Scheff
42 mins ago
1
@Scheff Oh man, I certainly won't ever forget this lesson...
– Phill
27 mins ago
@Phill I have collected some of them in my mind ...and sometimes tell my colleagues my stories of old about this... ;-)
– Scheff
26 mins ago
add a comment |
I've had a super frustrating bug in my code for the past few weeks. My code would work exactly as expected on my computer, but as soon as I farmed it out to the HPC server, it would produce weird results.
I've boiled it down to this: on my computer (iMac) the function abs() works with floating point numbers, but on the server abs() truncates it to an integer.
Example:
Server
abs(-1.1341234) = 1
My Mac
abs(-1.1341234) = 1.1341234
Now I know I can fix this by using fabs(), that's not the question. I looked at the versions of gcc on either machine and this is the output:
Server
g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/apps/software/GCCcore/5.4.0/libexec/gcc/x86_64-unknown-linux-gnu/5.4.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --enable-languages=c,c++,fortran --enable-lto --enable-checking=release --disable-multilib --enable-shared=yes --enable-static=yes --enable-threads=posix --enable-gold=default --enable-plugins --enable-ld --with-plugin-ld=ld.gold --prefix=/apps/software/GCCcore/5.4.0 --with-local-prefix=/apps/software/GCCcore/5.4.0 --enable-bootstrap --with-isl=/dev/shm/GCCcore/5.4.0/dummy-/gcc-5.4.0/stage2_stuff
Thread model: posix
gcc version 5.4.0 (GCC)
My Mac
g++ -v
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/include/c++/4.2.1
Apple LLVM version 10.0.1 (clang-1001.0.46.3)
Target: x86_64-apple-darwin18.5.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
So my question, why does abs() produce different results between gcc and clang? This issue literally cost me 3 weeks of progress, so as you can imagine I'm a little salty just now...
c++ gcc compilation clang
edited 12 mins ago
J. Antonio Perez
3,533926
asked 1 hour ago
PhillPhill
21415
I've had a super frustrating bug in my code for the past few weeks. My code would work exactly as expected on my computer, but as soon as I farmed it out to the HPC server, it would produce weird results.
I've boiled it down to this: on my computer (iMac) the function abs() works with floating point numbers, but on the server abs() truncates it to an integer.
Example:
Server
abs(-1.1341234) = 1
My Mac
abs(-1.1341234) = 1.1341234
Now I know I can fix this by using fabs(), that's not the question. I looked at the versions of gcc on either machine and this is the output:
Server
g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/apps/software/GCCcore/5.4.0/libexec/gcc/x86_64-unknown-linux-gnu/5.4.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --enable-languages=c,c++,fortran --enable-lto --enable-checking=release --disable-multilib --enable-shared=yes --enable-static=yes --enable-threads=posix --enable-gold=default --enable-plugins --enable-ld --with-plugin-ld=ld.gold --prefix=/apps/software/GCCcore/5.4.0 --with-local-prefix=/apps/software/GCCcore/5.4.0 --enable-bootstrap --with-isl=/dev/shm/GCCcore/5.4.0/dummy-/gcc-5.4.0/stage2_stuff
Thread model: posix
gcc version 5.4.0 (GCC)
My Mac
g++ -v
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/include/c++/4.2.1
Apple LLVM version 10.0.1 (clang-1001.0.46.3)
Target: x86_64-apple-darwin18.5.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
So my question, why does abs() produce different results between gcc and clang? This issue literally cost me 3 weeks of progress, so as you can imagine I'm a little salty just now...
c++ gcc compilation clang
c++ gcc compilation clang
edited 12 mins ago
J. Antonio Perez
3,533926
asked 1 hour ago
PhillPhill
21415
edited 12 mins ago
J. Antonio Perez
3,533926
asked 1 hour ago
PhillPhill
21415
edited 12 mins ago
J. Antonio Perez
3,533926
edited 12 mins ago
J. Antonio Perez
3,533926
edited 12 mins ago
J. Antonio Perez
3,533926
3,533926
asked 1 hour ago
PhillPhill
21415
asked 1 hour ago
PhillPhill
21415
asked 1 hour ago
PhillPhill
21415
21415
3
so as you can imagine I'm a little salty just now... Annoying but worth the lecture... This will make you very sensitive about these things. ;-) (I don't mean this offensive but rather as a "heads up". Every really annoying bug might at least produce a valuable experience. So, take it positively...)
– Scheff
42 mins ago
1
@Scheff Oh man, I certainly won't ever forget this lesson...
– Phill
27 mins ago
@Phill I have collected some of them in my mind ...and sometimes tell my colleagues my stories of old about this... ;-)
– Scheff
26 mins ago
add a comment |
3
so as you can imagine I'm a little salty just now... Annoying but worth the lecture... This will make you very sensitive about these things. ;-) (I don't mean this offensive but rather as a "heads up". Every really annoying bug might at least produce a valuable experience. So, take it positively...)
– Scheff
42 mins ago
1
@Scheff Oh man, I certainly won't ever forget this lesson...
– Phill
27 mins ago
@Phill I have collected some of them in my mind ...and sometimes tell my colleagues my stories of old about this... ;-)
– Scheff
26 mins ago
3
3
so as you can imagine I'm a little salty just now... Annoying but worth the lecture... This will make you very sensitive about these things. ;-) (I don't mean this offensive but rather as a "heads up". Every really annoying bug might at least produce a valuable experience. So, take it positively...)
– Scheff
42 mins ago
so as you can imagine I'm a little salty just now... Annoying but worth the lecture... This will make you very sensitive about these things. ;-) (I don't mean this offensive but rather as a "heads up". Every really annoying bug might at least produce a valuable experience. So, take it positively...)
– Scheff
42 mins ago
1
1
@Scheff Oh man, I certainly won't ever forget this lesson...
– Phill
27 mins ago
@Scheff Oh man, I certainly won't ever forget this lesson...
– Phill
27 mins ago
@Phill I have collected some of them in my mind ...and sometimes tell my colleagues my stories of old about this... ;-)
– Scheff
26 mins ago
@Phill I have collected some of them in my mind ...and sometimes tell my colleagues my stories of old about this... ;-)
– Scheff
26 mins ago
add a comment |
1 Answer
1
active
oldest
votes
You must use std::abs, which has overloads for the primitive types.
You are falling through to the C++ version in one case, and the old C version (which converts its parameters to integral types) in the other.
Things to avoid: (1) using namespace std; (here is why) and (2) not having the appropriate #includes to bring in the functionality you need. Don't rely on C++ standard library implementations to include files for you implicitly.
Some compilers will warn you of a "lossy" conversion if you set the warning level appropriately.
answered 59 mins ago
BathshebaBathsheba
183k27258386
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
You must use std::abs, which has overloads for the primitive types.
You are falling through to the C++ version in one case, and the old C version (which converts its parameters to integral types) in the other.
Things to avoid: (1) using namespace std; (here is why) and (2) not having the appropriate #includes to bring in the functionality you need. Don't rely on C++ standard library implementations to include files for you implicitly.
Some compilers will warn you of a "lossy" conversion if you set the warning level appropriately.
answered 59 mins ago
BathshebaBathsheba
183k27258386
add a comment |
You must use std::abs, which has overloads for the primitive types.
You are falling through to the C++ version in one case, and the old C version (which converts its parameters to integral types) in the other.
Things to avoid: (1) using namespace std; (here is why) and (2) not having the appropriate #includes to bring in the functionality you need. Don't rely on C++ standard library implementations to include files for you implicitly.
Some compilers will warn you of a "lossy" conversion if you set the warning level appropriately.
answered 59 mins ago
BathshebaBathsheba
183k27258386
add a comment |
You must use std::abs, which has overloads for the primitive types.
You are falling through to the C++ version in one case, and the old C version (which converts its parameters to integral types) in the other.
Things to avoid: (1) using namespace std; (here is why) and (2) not having the appropriate #includes to bring in the functionality you need. Don't rely on C++ standard library implementations to include files for you implicitly.
Some compilers will warn you of a "lossy" conversion if you set the warning level appropriately.
answered 59 mins ago
BathshebaBathsheba
183k27258386
You must use std::abs, which has overloads for the primitive types.
You are falling through to the C++ version in one case, and the old C version (which converts its parameters to integral types) in the other.
Things to avoid: (1) using namespace std; (here is why) and (2) not having the appropriate #includes to bring in the functionality you need. Don't rely on C++ standard library implementations to include files for you implicitly.
Some compilers will warn you of a "lossy" conversion if you set the warning level appropriately.
answered 59 mins ago
BathshebaBathsheba
183k27258386
edited 5 mins ago
answered 59 mins ago
BathshebaBathsheba
183k27258386
answered 59 mins ago
BathshebaBathsheba
183k27258386
answered 59 mins ago
BathshebaBathsheba
183k27258386
183k27258386
add a comment |
add a comment |
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3
so as you can imagine I'm a little salty just now... Annoying but worth the lecture... This will make you very sensitive about these things. ;-) (I don't mean this offensive but rather as a "heads up". Every really annoying bug might at least produce a valuable experience. So, take it positively...)
– Scheff
42 mins ago
1
@Scheff Oh man, I certainly won't ever forget this lesson...
– Phill
27 mins ago
@Phill I have collected some of them in my mind ...and sometimes tell my colleagues my stories of old about this... ;-)
– Scheff
26 mins ago