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Why is C++ initial allocation so much larger than C's?
How much faster is C++ than C#?Why do we need virtual functions in C++?Why should C++ programmers minimize use of 'new'?Why are elementwise additions much faster in separate loops than in a combined loop?Why is reading lines from stdin much slower in C++ than Python?Why is processing a sorted array faster than processing an unsorted array?Why should I use a pointer rather than the object itself?C++ code for testing the Collatz conjecture faster than hand-written assembly - why?C vs C++ compilation incompatibility - does not name a typeWhy is 2 * (i * i) faster than 2 * i * i in Java?
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When using the same code, simply changing the compiler (from a C compiler to a C++ compiler) will change how much memory is allocated. I'm not quite sure why this is and would like to understand it more. So far the best response I've gotten is "probably the IO streams", which isn't very descriptive and makes me wonder about the "you don't pay for what you don't use" aspect of C++.
I'm using the clang and gcc compilers, versions 7.0.1-8 and 8.3.0-6 respectively. My system is running on Debian 10 (Buster), latest. The benchmarks are done via Valgrind Massif.
#include <stdio.h>
int main()
printf("Hello, world!n");
return 0;
The code used does not change, but whether I compile as C or as C++ changes the results of the Valgrind benchmark. The values remain consistent across compilers, however.
The runtime allocations (peak) for the program go as follows:
- GCC (C): 1,032 bytes (1KB)
- G++ (C++): 73,744 bytes, (~74kb)
- Clang (C): 1,032 bytes (1KB)
- Clang++ (C++): 73,744 bytes (~74kb)
For compiling, I use the following commands:
clang -O3 -o c-clang ./main.c
gcc -O3 -o c-gcc ./main.c
clang++ -O3 -o cpp-clang ./main.cpp
g++ -O3 -o cpp-gcc ./main.cpp
For Valgrind, I run valgrind --tool=massif --massif-out-file=m_compiler_lang ./compiler-lang on each compiler and language, then ms_print for displaying the peaks.
Am I doing something wrong here?
c++ c benchmarking
asked 9 hours ago
RerumuRerumu
485 bronze badges
New contributor
Rerumu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
|
show 4 more comments
When using the same code, simply changing the compiler (from a C compiler to a C++ compiler) will change how much memory is allocated. I'm not quite sure why this is and would like to understand it more. So far the best response I've gotten is "probably the IO streams", which isn't very descriptive and makes me wonder about the "you don't pay for what you don't use" aspect of C++.
I'm using the clang and gcc compilers, versions 7.0.1-8 and 8.3.0-6 respectively. My system is running on Debian 10 (Buster), latest. The benchmarks are done via Valgrind Massif.
#include <stdio.h>
int main()
printf("Hello, world!n");
return 0;
The code used does not change, but whether I compile as C or as C++ changes the results of the Valgrind benchmark. The values remain consistent across compilers, however.
The runtime allocations (peak) for the program go as follows:
- GCC (C): 1,032 bytes (1KB)
- G++ (C++): 73,744 bytes, (~74kb)
- Clang (C): 1,032 bytes (1KB)
- Clang++ (C++): 73,744 bytes (~74kb)
For compiling, I use the following commands:
clang -O3 -o c-clang ./main.c
gcc -O3 -o c-gcc ./main.c
clang++ -O3 -o cpp-clang ./main.cpp
g++ -O3 -o cpp-gcc ./main.cpp
For Valgrind, I run valgrind --tool=massif --massif-out-file=m_compiler_lang ./compiler-lang on each compiler and language, then ms_print for displaying the peaks.
Am I doing something wrong here?
c++ c benchmarking
asked 9 hours ago
RerumuRerumu
485 bronze badges
New contributor
Rerumu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
4
To begin with, how are you building? What options do you use? And how do you measure? How do you run Valgrind?
– Some programmer dude
9 hours ago
This is C, not C++. C that compiles with a C++ compiler is just malformed C++. Regardless, C++ has more memory overhead than C as you can already tell.
– bigwillydos
9 hours ago
Hypothesis: this allocation comes from the standard library. There's more in the C++ standard library. I don't know where 73kb extra comes from, but maybe loading a shared library counts as an allocation.
– Justin
9 hours ago
5
If I remember correctly, modern C++ compilers have to an exception model where there is no performance hit to entering atryblock at the expense of a larger memory footprint, maybe with a jump table or something. Maybe try compiling without exceptions and see what impact that has. Edit : In fact, iteratively try disabling various c++ features to see what impact that has on the memory footprint.
– François Andrieux
9 hours ago
1
When compiling withclang++ -xcinstead ofclang, the same allocation was there, which strongly suggests its due to linked libraries
– Justin
9 hours ago
|
show 4 more comments
When using the same code, simply changing the compiler (from a C compiler to a C++ compiler) will change how much memory is allocated. I'm not quite sure why this is and would like to understand it more. So far the best response I've gotten is "probably the IO streams", which isn't very descriptive and makes me wonder about the "you don't pay for what you don't use" aspect of C++.
I'm using the clang and gcc compilers, versions 7.0.1-8 and 8.3.0-6 respectively. My system is running on Debian 10 (Buster), latest. The benchmarks are done via Valgrind Massif.
#include <stdio.h>
int main()
printf("Hello, world!n");
return 0;
The code used does not change, but whether I compile as C or as C++ changes the results of the Valgrind benchmark. The values remain consistent across compilers, however.
The runtime allocations (peak) for the program go as follows:
- GCC (C): 1,032 bytes (1KB)
- G++ (C++): 73,744 bytes, (~74kb)
- Clang (C): 1,032 bytes (1KB)
- Clang++ (C++): 73,744 bytes (~74kb)
For compiling, I use the following commands:
clang -O3 -o c-clang ./main.c
gcc -O3 -o c-gcc ./main.c
clang++ -O3 -o cpp-clang ./main.cpp
g++ -O3 -o cpp-gcc ./main.cpp
For Valgrind, I run valgrind --tool=massif --massif-out-file=m_compiler_lang ./compiler-lang on each compiler and language, then ms_print for displaying the peaks.
Am I doing something wrong here?
c++ c benchmarking
asked 9 hours ago
RerumuRerumu
485 bronze badges
New contributor
Rerumu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
When using the same code, simply changing the compiler (from a C compiler to a C++ compiler) will change how much memory is allocated. I'm not quite sure why this is and would like to understand it more. So far the best response I've gotten is "probably the IO streams", which isn't very descriptive and makes me wonder about the "you don't pay for what you don't use" aspect of C++.
I'm using the clang and gcc compilers, versions 7.0.1-8 and 8.3.0-6 respectively. My system is running on Debian 10 (Buster), latest. The benchmarks are done via Valgrind Massif.
#include <stdio.h>
int main()
printf("Hello, world!n");
return 0;
The code used does not change, but whether I compile as C or as C++ changes the results of the Valgrind benchmark. The values remain consistent across compilers, however.
The runtime allocations (peak) for the program go as follows:
- GCC (C): 1,032 bytes (1KB)
- G++ (C++): 73,744 bytes, (~74kb)
- Clang (C): 1,032 bytes (1KB)
- Clang++ (C++): 73,744 bytes (~74kb)
For compiling, I use the following commands:
clang -O3 -o c-clang ./main.c
gcc -O3 -o c-gcc ./main.c
clang++ -O3 -o cpp-clang ./main.cpp
g++ -O3 -o cpp-gcc ./main.cpp
For Valgrind, I run valgrind --tool=massif --massif-out-file=m_compiler_lang ./compiler-lang on each compiler and language, then ms_print for displaying the peaks.
Am I doing something wrong here?
c++ c benchmarking
c++ c benchmarking
asked 9 hours ago
RerumuRerumu
485 bronze badges
New contributor
Rerumu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 9 hours ago
RerumuRerumu
485 bronze badges
New contributor
Rerumu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 9 hours ago
Rerumu
asked 9 hours ago
RerumuRerumu
485 bronze badges
New contributor
Rerumu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 9 hours ago
RerumuRerumu
485 bronze badges
asked 9 hours ago
RerumuRerumu
485 bronze badges
485 bronze badges
New contributor
Rerumu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Rerumu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
4
To begin with, how are you building? What options do you use? And how do you measure? How do you run Valgrind?
– Some programmer dude
9 hours ago
This is C, not C++. C that compiles with a C++ compiler is just malformed C++. Regardless, C++ has more memory overhead than C as you can already tell.
– bigwillydos
9 hours ago
Hypothesis: this allocation comes from the standard library. There's more in the C++ standard library. I don't know where 73kb extra comes from, but maybe loading a shared library counts as an allocation.
– Justin
9 hours ago
5
If I remember correctly, modern C++ compilers have to an exception model where there is no performance hit to entering atryblock at the expense of a larger memory footprint, maybe with a jump table or something. Maybe try compiling without exceptions and see what impact that has. Edit : In fact, iteratively try disabling various c++ features to see what impact that has on the memory footprint.
– François Andrieux
9 hours ago
1
When compiling withclang++ -xcinstead ofclang, the same allocation was there, which strongly suggests its due to linked libraries
– Justin
9 hours ago
|
show 4 more comments
4
To begin with, how are you building? What options do you use? And how do you measure? How do you run Valgrind?
– Some programmer dude
9 hours ago
This is C, not C++. C that compiles with a C++ compiler is just malformed C++. Regardless, C++ has more memory overhead than C as you can already tell.
– bigwillydos
9 hours ago
Hypothesis: this allocation comes from the standard library. There's more in the C++ standard library. I don't know where 73kb extra comes from, but maybe loading a shared library counts as an allocation.
– Justin
9 hours ago
5
If I remember correctly, modern C++ compilers have to an exception model where there is no performance hit to entering atryblock at the expense of a larger memory footprint, maybe with a jump table or something. Maybe try compiling without exceptions and see what impact that has. Edit : In fact, iteratively try disabling various c++ features to see what impact that has on the memory footprint.
– François Andrieux
9 hours ago
1
When compiling withclang++ -xcinstead ofclang, the same allocation was there, which strongly suggests its due to linked libraries
– Justin
9 hours ago
4
4
To begin with, how are you building? What options do you use? And how do you measure? How do you run Valgrind?
– Some programmer dude
9 hours ago
To begin with, how are you building? What options do you use? And how do you measure? How do you run Valgrind?
– Some programmer dude
9 hours ago
This is C, not C++. C that compiles with a C++ compiler is just malformed C++. Regardless, C++ has more memory overhead than C as you can already tell.
– bigwillydos
9 hours ago
This is C, not C++. C that compiles with a C++ compiler is just malformed C++. Regardless, C++ has more memory overhead than C as you can already tell.
– bigwillydos
9 hours ago
Hypothesis: this allocation comes from the standard library. There's more in the C++ standard library. I don't know where 73kb extra comes from, but maybe loading a shared library counts as an allocation.
– Justin
9 hours ago
Hypothesis: this allocation comes from the standard library. There's more in the C++ standard library. I don't know where 73kb extra comes from, but maybe loading a shared library counts as an allocation.
– Justin
9 hours ago
5
5
If I remember correctly, modern C++ compilers have to an exception model where there is no performance hit to entering a
try block at the expense of a larger memory footprint, maybe with a jump table or something. Maybe try compiling without exceptions and see what impact that has. Edit : In fact, iteratively try disabling various c++ features to see what impact that has on the memory footprint.– François Andrieux
9 hours ago
If I remember correctly, modern C++ compilers have to an exception model where there is no performance hit to entering a
try block at the expense of a larger memory footprint, maybe with a jump table or something. Maybe try compiling without exceptions and see what impact that has. Edit : In fact, iteratively try disabling various c++ features to see what impact that has on the memory footprint.– François Andrieux
9 hours ago
1
1
When compiling with
clang++ -xc instead of clang, the same allocation was there, which strongly suggests its due to linked libraries– Justin
9 hours ago
When compiling with
clang++ -xc instead of clang, the same allocation was there, which strongly suggests its due to linked libraries– Justin
9 hours ago
|
show 4 more comments
1 Answer
1
active
oldest
votes
The heap usage comes from the C++ standard library. It allocates memory for internal library use on startup. If you don't link against it, there should be zero difference between the C and C++ version. With GCC and Clang, you can compile the file with:
g++ -Wl,--as-needed main.cpp
This will instruct the linker to not link against unused libraries. In your example code, the C++ library is not used, so it should not link against the C++ standard library.
You can also test this with the C file. If you compile with:
gcc main.c -lstdc++
The heap usage will reappear, even though you've built a C program.
answered 8 hours ago
Nikos C.Nikos C.
38.6k5 gold badges43 silver badges74 bronze badges
On seeing this answer, my first thought is, "If this flag helps reduce unneeded overhead, why isn't it on by default?". Is there a good answer to that?
– Nat
13 mins ago
add a comment |
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The heap usage comes from the C++ standard library. It allocates memory for internal library use on startup. If you don't link against it, there should be zero difference between the C and C++ version. With GCC and Clang, you can compile the file with:
g++ -Wl,--as-needed main.cpp
This will instruct the linker to not link against unused libraries. In your example code, the C++ library is not used, so it should not link against the C++ standard library.
You can also test this with the C file. If you compile with:
gcc main.c -lstdc++
The heap usage will reappear, even though you've built a C program.
answered 8 hours ago
Nikos C.Nikos C.
38.6k5 gold badges43 silver badges74 bronze badges
On seeing this answer, my first thought is, "If this flag helps reduce unneeded overhead, why isn't it on by default?". Is there a good answer to that?
– Nat
13 mins ago
add a comment |
The heap usage comes from the C++ standard library. It allocates memory for internal library use on startup. If you don't link against it, there should be zero difference between the C and C++ version. With GCC and Clang, you can compile the file with:
g++ -Wl,--as-needed main.cpp
This will instruct the linker to not link against unused libraries. In your example code, the C++ library is not used, so it should not link against the C++ standard library.
You can also test this with the C file. If you compile with:
gcc main.c -lstdc++
The heap usage will reappear, even though you've built a C program.
answered 8 hours ago
Nikos C.Nikos C.
38.6k5 gold badges43 silver badges74 bronze badges
On seeing this answer, my first thought is, "If this flag helps reduce unneeded overhead, why isn't it on by default?". Is there a good answer to that?
– Nat
13 mins ago
add a comment |
The heap usage comes from the C++ standard library. It allocates memory for internal library use on startup. If you don't link against it, there should be zero difference between the C and C++ version. With GCC and Clang, you can compile the file with:
g++ -Wl,--as-needed main.cpp
This will instruct the linker to not link against unused libraries. In your example code, the C++ library is not used, so it should not link against the C++ standard library.
You can also test this with the C file. If you compile with:
gcc main.c -lstdc++
The heap usage will reappear, even though you've built a C program.
answered 8 hours ago
Nikos C.Nikos C.
38.6k5 gold badges43 silver badges74 bronze badges
The heap usage comes from the C++ standard library. It allocates memory for internal library use on startup. If you don't link against it, there should be zero difference between the C and C++ version. With GCC and Clang, you can compile the file with:
g++ -Wl,--as-needed main.cpp
This will instruct the linker to not link against unused libraries. In your example code, the C++ library is not used, so it should not link against the C++ standard library.
You can also test this with the C file. If you compile with:
gcc main.c -lstdc++
The heap usage will reappear, even though you've built a C program.
answered 8 hours ago
Nikos C.Nikos C.
38.6k5 gold badges43 silver badges74 bronze badges
edited 8 hours ago
answered 8 hours ago
Nikos C.Nikos C.
38.6k5 gold badges43 silver badges74 bronze badges
answered 8 hours ago
Nikos C.Nikos C.
38.6k5 gold badges43 silver badges74 bronze badges
answered 8 hours ago
Nikos C.Nikos C.
38.6k5 gold badges43 silver badges74 bronze badges
38.6k5 gold badges43 silver badges74 bronze badges
On seeing this answer, my first thought is, "If this flag helps reduce unneeded overhead, why isn't it on by default?". Is there a good answer to that?
– Nat
13 mins ago
add a comment |
On seeing this answer, my first thought is, "If this flag helps reduce unneeded overhead, why isn't it on by default?". Is there a good answer to that?
– Nat
13 mins ago
On seeing this answer, my first thought is, "If this flag helps reduce unneeded overhead, why isn't it on by default?". Is there a good answer to that?
– Nat
13 mins ago
On seeing this answer, my first thought is, "If this flag helps reduce unneeded overhead, why isn't it on by default?". Is there a good answer to that?
– Nat
13 mins ago
add a comment |
Rerumu is a new contributor. Be nice, and check out our Code of Conduct.
Rerumu is a new contributor. Be nice, and check out our Code of Conduct.
Rerumu is a new contributor. Be nice, and check out our Code of Conduct.
Rerumu is a new contributor. Be nice, and check out our Code of Conduct.
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4
To begin with, how are you building? What options do you use? And how do you measure? How do you run Valgrind?
– Some programmer dude
9 hours ago
This is C, not C++. C that compiles with a C++ compiler is just malformed C++. Regardless, C++ has more memory overhead than C as you can already tell.
– bigwillydos
9 hours ago
Hypothesis: this allocation comes from the standard library. There's more in the C++ standard library. I don't know where 73kb extra comes from, but maybe loading a shared library counts as an allocation.
– Justin
9 hours ago
5
If I remember correctly, modern C++ compilers have to an exception model where there is no performance hit to entering a
tryblock at the expense of a larger memory footprint, maybe with a jump table or something. Maybe try compiling without exceptions and see what impact that has. Edit : In fact, iteratively try disabling various c++ features to see what impact that has on the memory footprint.– François Andrieux
9 hours ago
1
When compiling with
clang++ -xcinstead ofclang, the same allocation was there, which strongly suggests its due to linked libraries– Justin
9 hours ago